Effect of main elements (Zn、Mg and Cu) on the microstructure, castability and mechanical properties of 7xxx series aluminum alloys with Zr and Sc

Liu W., Liu Y., Cheng Y., Chen L., Yu L., Yi X., Duan H.

Size-dependent yield strength is a common feature observed in miniaturized crystalline metallic samples, and plenty of studies have been conducted in experiments and numerical simulations to explore the underlying mechanism. However, the transition in yield strength from bulklike to size-affected behavior has received less attention. Here a unified theoretical model is proposed to probe the yield strength of crystalline metallic materials with sample size from nanoscale to macroscale. We show that the transition in yield strength versus size can be fully explained by the competition between the stresses required for dislocation source activation and dislocation motion, which is regulated by dislocation density, irradiation defect, grain boundary, and so on. Based on various grain boundary densities, the extended Hall-Petch relation, incorporated into the unified model, captures the reverse size effect for polycrystalline samples. The proposed model predictions agree well with reported experimental measurements of various specimens, including the prestrained nickel, irradiated copper, ultrafine grain tungsten, and so on.

Li Y., Zhang Z.R., Zhao Z.Y., Li H.X., Katgerman L., Zhang J.S., Zhuang L.Z.

New 7xxx aluminum alloys with high alloying contents are being designed, which could induce serious hot tearing defects during direct-chill (DC) casting. Among all factors affecting hot tearing of 7xxx alloys, undoubtedly alloying elements play a significant role. In this study, the effect of main alloying elements (Zn, Mg, and Cu) on hot tearing of grain-refined Al-xZn-yMg-zCu alloys was investigated by a dedicated hot tearing rating apparatus simulating the DC-casting process. It was found that the minimum and maximum hot tearing susceptibilities occur for 4 to 6 and 9 wt pct Zn, respectively, indicating the complicated effect of Zn content. The hot tearing resistance of grain-refined Al-9Zn-yMg-zCu alloys is enhanced with increasing Mg content but is deteriorated with increasing Cu content. This can be attributed to the interaction of the thermal stresses, melt feeding, and final eutectics. The observed tendencies of the main alloying elements on hot tearing were also confirmed for four commercial 7xxx alloys. In addition, both the load value at non-equilibrium solidus and the SKK criterion proposed by Suyitno et al. using measured load developments were found to be good indicators in predicting hot tearing susceptibility. This study can provide a beneficial guide in designing 7xxx alloys considering the potential occurrence of hot cracks beforehand.

Zhao H., Gault B., Ponge D., Raabe D., De Geuser F.

Atom probe tomography enables precise quantification of the composition of second phase particles from their early stages, leading to improved understanding of the thermodynamic and kinetic mechanisms of phase formation and quantify structure-property relationships. Here we demonstrate how approaches developed for small-angle scattering can be adapted to atom probe tomography. By exploiting nearest-neighbor distributions and radial distribution function, we introduce a parameter free methodology to efficiently extract information such as particle size, composition, volume fraction, number density and inter-particle distance. We demonstrate the strength of this approach in the analysis of a precipitation-hardened model Al-Zn-Mg-Cu high-strength lightweight alloy.

Zuo J., Hou L., Shi J., Cui H., Zhuang L., Zhang J.

An improved low-temperature thermo-mechanical treatment (LTMT based on DYA: dynamic aging) aiming to discover the action of deformation-induced precipitation to microstructures and corrosion resistance was proposed that included a conventional T6 peak aging (120 °C/24 h) and a subsequent dynamic aging. Its influence on mechanical properties, electrochemical behavior and intergranular/exfoliation corrosion resistance of 7055 Al alloy were investigated by tensile testing, polarization curve, intergranular/exfoliation corrosion testing combined with optical microscope and transmission electron microscope observation. It shows that after the conventional T6 peak aging, the matrix precipitates were fine and dispersive while the grain boundary precipitates were coarse and continuously distributed. With the introduction of dynamic aging, the grain boundary precipitates become discontinuously distributed gradually without much coarsening of matrix precipitates. As a result, the LTMT process can improve intergranular/exfoliation corrosion resistances without sacrificing strength that could be attributed to the discontinuous grain boundary precipitates and fine dispersed matrix precipitates, respectively. The improved corrosion resistance was also confirmed by polarization curves and conductivity test. It indicates that the present LTMT process may be a good alternative to produce heat-treatable Al alloy sheets with good strength and corrosion resistance.

Shin J., Kim T., Kim D., Kim D., Kim K.

To develop an aluminum alloy that combines excellent mechanical properties with good castability for near-net-shape casting of automotive structural parts, new Cu–free medium Mg 7xxx aluminum alloys with minor Zr (0.1%) and Ti (0, 0.1, and 0.2%) (all contents in wt% unless stated otherwise) elemental content were investigated as potential candidates. The effects of a vulnerable temperature interval and grain refinement on the hot tearing susceptibility (HTS) were investigated in this work to prevent hot tearing. Al–6Zn–(1.3–1.5)Mg–0.1Zr–(0.1–0.2)Ti alloys show 140–150% of ultimate tensile strength (370–390 MPa), 150–180% of elongation (10–12%), 60–80% of medium-thick-wall fluidity, and equivalent thin-wall fluidity, compared to the respective properties of the commercial A356 alloy. Medium-thick-wall fluidity depended on the heat release upon solidification of the alloy investigated, and thin-wall fluidity depended on the surface energy of the alloy in molten state. When the Ti content was increased, a concave variation in the medium-thick-wall fluidity and a monotonic increase in the thin-wall fluidity were observed. In terms of hot tearing, Ti addition led to a decrease in the HTS, which eventually reached zero. By adding 3% Si, hot tearing could be prevented; however, at the same time, elongation was found to decrease to less than 4%. The grain size reduction and morphology alteration due to the combined addition of 0.2% Ti and 0.1% Zr led to an improvement in castability because of a delay in crystal coherency, decrease in solidification time and vulnerable time period, and suppression of Fe-containing intermetallic and T phase crystallization.

Bai Q., Li H., Du Q., Zhang J., Zhuang L.

The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter f GBWL, i.e., the fraction of grain boundaries covered by liquid phase.

Li X., Cai Q., Zhao B., Xiao Y., Li B.

A novel grain refiner consisting of nanoparticulate TiN suspended in a Ti metal powder (abbr. TiN/Ti refiner) was prepared by high energy ball milling. The effect of the TiN/Ti refiner addition contents on microstructures and properties of Al-Zn-Mg-Cu alloy was investigated in detail. The results show that the TiN/Ti refiner addition changes the α(Al) matrix morphology of the modified Al-Zn-Mg-Cu alloy from dendrite to equiaxed crystaline. With increasing TiN/Ti refiner addition contents from 0 wt.% to 0.5 wt.%, the average grain size of Al-Zn-Mg-Cu alloy decreases sharply from 400 μm to 78.5 μm. The SEM, EDS, XRD, and DSC results demonstrate that secondary phases of the modified Al-Zn-Mg-Cu alloy contain three kinds of intermetallic phases: σ[Mg(Zn, Cu, Al)2], θ(Al2Cu) and iron containing intermetallic of Al7Cu2Fe. With refined α(Al) grains, secondary phases are dispersed, refined and distributed uniformly. With increasing TiN/Ti addition contents from 0 wt.% to 0.5 wt.%, the yield strength, tensile strength and Vickers hardness of the modified Al-Zn-Mg-Cu alloys enhance from 36.6 MPa to 74.6 MPa, from 175 MPa to 235 MPa and from 118 HV to 152.5 HV, respectively. In addition, the yield strength σy, tensile strength σb and Vickers hardness Hv of the modified Al-Zn-Mg-Cu alloys show Hall-Peteh dependences on the grain size D. A typical interdendritic fracture is observed on the tensile fracture surface of the as-cast Al-Zn-Mg-Cu alloy. Grain boundary and secondary phase regions act as an easy path for crack propagation.

Wen K., Fan Y., Wang G., Jin L., Li X., Li Z., Zhang Y., Xiong B.

In the present work, the influence of one-step and two-step aging treatments on hardness, electrical conductivity and mechanical properties of a high Zn-containing Al-Zn-Mg-Cu alloy is investigated and detailed aging parameters subjected to various aging tempers, i.e., T6, T79, T76, T74 and T73, are proposed. The nanoscale precipitates under different tempers are qualitatively investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) techniques. Based on the precipitate observations, precipitate size distributions and neighbor precipitates distances are extracted from bright-field TEM images projected along 〈110〉 Al orientation with the aid of an imaging analysis. The results show that with the deepening of aging degree, the conductivity of one-step and two-step aging increase continuously while the hardness increases for one-step aging and decreases for two-step aging at the second preservation. The tensile strength decreases as the aging degree deepens and the yield strength shows a similar trend. In addition, as the degree of over-aging deepens, the precipitate size distribution interval becomes broader, the average precipitate size turns larger and the average distance of neighbor precipitates also becomes greater. The influence of precipitates on mechanical properties is discussed.

Shin S., Yeom G., Kwak T., Park I.

The microstructure and mechanical properties of newly developed Al–35Zn cast alloys with TiB refiner addition were evaluated by X-ray diffractometry, optical microscopy, and scanning electron microscopy coupled with energy dispersive spectrometry. The microstructure of these alloys featured α-Al dendrites surrounded by Al–Zn (α + η) eutectic structures. After the addition of TiB refiner, the alloy grain sizes decreased, and its morphology abruptly changed from dendritic to equiaxed grains. Such an improved microstructure of the modified alloys was accompanied by a significant increase in the tensile strength and elongation percentage compared to those of the Al–Zn or Zn–Al-based alloys. The results showed that with the increase of TiB content up to 0.05%, the morphology of α-Al dendrites and α + η phases changed from coarse dendrite and lamellar structures into independent and fine ones. Based on these results, the effect of TiB refiner addition on the microstructure and mechanical properties of the Al–35Zn binary alloys was investigated.

Shin S., Lim K., Park I.

Al–Zn-based alloys with high strength of >470 MPa for die-casting were successfully fabricated without melt modification and post-casting heat treatment. We designed Al-based alloys containing more than 20 wt% of Zn for the die-casting process. The matrix phase of the alloy was angular α-Al surrounded by a very fine lamellar structure of α-Al and η-Zn. The average grain size of the matrix was relatively small (∼25 μm), and a complex network of eutectoid α + η, supersaturated η, β, and Cu-related intermetallic particles formed at the grain boundaries or non-equilibrium solidification phases. This microstructural feature obtained by the addition of more than 20 wt% Zn significantly enhanced the strength of the Al–Zn-based alloys. Furthermore, we investigated the fluidity and wear properties of the developed alloys, which improved as the Zn content was increased.

Li Y., Bai Q.L., Liu J.C., Li H.X., Du Q., Zhang J.S., Zhuang L.Z.

The influences of grain size and morphology on the hot tearing susceptibility of AA7050 alloy inoculated with Al-5Ti-1B master alloy were investigated by the authors. It was found that with the optimal addition of Al-5Ti-1B, coarse columnar grains were transformed into fine globular equiaxed grains. Moreover, due to the changes of grain size and morphology, the hot tearing susceptibility was decreased remarkably, which was attributed to the lower mechanical coherency temperature, better feeding ability, lower strain, and strain rate imposed to the mushy zone and more meandering propagation paths of hot tears. But the excess Al-5Ti-1B additions did not affect the grain structure, and greatly promoted hot tearing susceptibility due to the agglomerations of secondary phase particles from Al-5Ti-1B master alloy. The formation of massive secondary phases at grain boundaries hindered the interdendritic liquid flow and substantially deteriorated the feeding ability in the last stage of solidification. Meanwhile, TiB2 agglomerates would also act as stress raisers and cause the formation of voids. The contraction and load behaviors of AA7050 alloy influenced by grain size and morphology would be explored and connected with the hot tearing occurrence in this study.

Easton M.A., Qian M., Prasad A., StJohn D.H.

Grain refinement leads, in general, to a decreased tendency to hot tearing, a more dispersed and refined porosity distribution, and improved directional feeding characteristics during solidification. Reduced as-cast grain size can also lead to improved mechanical properties and wrought processing by reducing the recrystallized grain size and achieving a fully recrystallized microstructure. It is now well established that the two key factors controlling grain refinement are the nucleant particles including their potency, size distribution and particle number density, and the rate of development of growth restriction, Q, generated by the alloy chemistry which establishes the undercooling needed to trigger nucleation events and facilitates their survival. The theories underpinning our current understanding of nucleation and grain formation are presented. The application of the latest theories to the light alloys of Al, Mg and Ti is explored as well as their applicability to a range of casting and solidification environments. In addition, processing by the application of physical processes such as external fields and additive manufacturing is discussed. To conclude, the current challenges for the development of reliable grain refining technologies for difficult to refine alloy systems are presented.

Pozdniakov A.V., Zolotorevskiy V.S., Mamzurina O.I.

Seyed Ebrahimi S.H., Aghazadeh J., Dehghani K., Emamy M., Zangeneh S.

The aim of the present study is to investigate the effect of Al−5Ti−1B grain refiner on the microstructure, hardness and tensile properties of a new Zn-rich Al−Zn−Mg−Cu alloy. The microstructural observations revealed that Ti addition refines the grain size (up to 95%) and dispersion of the second phase and subsequently forms rosette-shape grains. In addition, the grain refinement by Al3Ti particles resulted in an increase in the area fraction of the recrystallized regions as compared to unrefined specimens. After grain refinement and thermomechanical processes, the improvements of the tensile strength, yield strength and elongation values were nearly 33%, 25% and 1930% respectively, when compared to as-cast specimens. Computer simulation used to determine the strain and stress patterns showed a plastic strain gradient from the edge to the center of the hot worked specimen. The microscopic examination of the fracture surfaces showed dimple-like mechanism in deformed specimens while the presence of coarse eutectic constituent in interdendritic regions was responsible for brittle fracture in not deformed ones.

Yu H., Wang M., Jia Y., Xiao Z., Chen C., Lei Q., Li Z., Chen W., Zhang H., Wang Y., Cai C.

• Spray deposition process was used to produce Al alloys with excellent performance. • The deposited alloys exhibited a high strength of 690 MPa and elongation up to 17.2%. • The η′ phase was coherent with α-Al and their orientation relationship was studied. • The interface misfits and the transition matrixes of two phases were calculated. The mechanical properties and microstructure of large-scale Al–Zn–Mg–Cu alloys fabricated by spray deposition/rapid solidification technology were investigated in detail. The as-extruded alloys under peak-aging temper exhibited ultimate tensile strength (UTS), yield strength (YS) and elongation of 690 MPa, 638 MPa and 17.2%, respectively. The simultaneous coexisting of high strength and large tensile ductility of the alloys were achieved in our experiment. It was considered that the high-density nano-precipitates distributed uniformly in the peak-aged alloys may be responsible for the high strength and improved ductility. Orientation relationship between η′ precipitates and α-Al matrix were verified by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction patterns (SADPs) observations. The η′ phases in the alloy were fully coherent with the aluminum matrix, with the orientation relationship of ( 1 0 1 ¯ 0 ) η ′ / / { 1 1 0 } Al and [ 1 ¯ 2 1 ¯ 0 ] η ′ / / < 1 ¯ 1 2 > Al . The relationship between the lattice parameters of η ′ phase and the related plane-spacing of the aluminum were a η ′ = 3 d ( 1 1 2 ) Al and c η ′ = 6 d ( 1 1 1 ) Al . Based on obtained orientation relationship, the transition matrix of η′ phases were also calculated.

Li P., Sui Y., Shen W., Jiang Y., Li W.

Lin Y., Wang L.

Zhao J., Zhang R., Li R., Liu Y., Bai S., Zhao X., Sang J., Huang J., Liu C., Liu X., Du F.

High temperature tensile properties and long-term thermal stability play an important role in practical applications of Al-Zn-Mg-Cu alloys. In order to evaluate the effect of Er addition on the properties of an Al-Zn-Mg-Cu alloy as potential high temperature structural materials, the heat resistance properties of an Al-Zn-Mg-Cu alloy were investigated at various temperatures. After high temperature tensile testing and long periods of heat exposure testing, the microstructures of Al-Zn-Cu-Mg alloys with and without small Er addition is intentionally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and quantitative transmission electron microscopy (TEM) characterization to explore the potential effect of Er on the tensile properties. The experimental results reveal that the heat resistance of T76-tempered Al-Zn-Cu-Mg alloy is obviously improved by adding trace Er. The Al8Cu4Er phase is found to segregate at the localized regions along grain boundaries and strengthens the grain boundaries at elevated temperatures. The η′ and η precipitation is obviously promoted by adding trace Er, and dispersed nano-sized Al3(Er, Zr) precipitates were formed in the Er-containing alloys after homogenization, thereby enhancing the strength of Al-Zn-Mg-Cu. In addition, precipitates in both alloys gradually coarsen with the increase in thermal exposure temperature and the extension of thermal exposure time. The influence of precipitates on mechanical properties of the investigatived alloy after thermal exposure is also discussed.

Yu C., Wang Y., Yuan X., Kang N., Ke L., Jia C., Yuan T., Li R.

Li Q., Wen X., Gao Q., Li J., Zhang X., Qiao J.

Peng J., Yuan S., Wang W., Gan P., Ji J., Zeng J.

Li P., Sui Y., Jiang Y., Yuan Y., Yang H., Yang J.

Gao Y., Dong B., Yang H., Yao X., Shu S., Kang J., Meng J., Luo C., Wang C., Cao K., Qiao J., Zhu M., Qiu F., Jiang Q.

For the development of new energy automobile industry and the trend of automobile lightweight have put forward a huge demand for high-strength lightweight materials, so developing high strength aluminum alloys is particularly momentous. As the most widely used aluminum alloy, 6000 series aluminum alloys (Al–Mg–Si alloys) have the advantages such as better mechanical properties, outstanding welding properties, excellent formability and fine processing capability, and therefore have obtained great attention as the structural materials. In addition, the Al–Mg–Si alloys with low density and corrosion resistance not only reduce the total weight of the car, but also extend the service life when subjected to chemical corrosion, which effectively achieve energy saving and emission reduction. This paper summarizes the research progress of 6000 series aluminum alloys, in particular, and reviews the methods of microalloying and particle strengthening, and their effects on the microstructure and properties of the alloy, thus providing a reference for the subsequent development of high-performance aluminum alloys in automobile and aerospace industries.

Higa R., Fujihara H., Toda H., Kobayashi M., Ebihara K., Takeuchi A.

Kim M., Kim J.

Recent advances in the leisure boat industry have spurred demand for improved materials for propeller manufacturing, particularly high-strength aluminum alloys. While traditional Al-Si alloys like A356 are commonly used due to their excellent castability, they have limited mechanical properties. In contrast, 7xxx series alloys (Al−Zn−Mg−Cu based) offer superior mechanical characteristics but present significant casting challenges, including hot-tearing susceptibility (HTS). This study investigates the optimization of 7xxx series aluminum alloys for low-pressure die-casting (LPDC) processes to enhance propeller performance and durability. Using a constrained rod-casting (CRC) method and finite element simulations, we evaluated the HTS of various alloy compositions. The results indicate that increasing Zn and Cu contents generally increase HTS, while a sufficient Mg content of 2 wt.% mitigates this effect. Two optimized quaternary Al−Zn−Mg−Cu alloys with relatively low HTS were selected for LPDC propeller production. Simulation and experimental results demonstrated the effectiveness of the proposed alloy compositions, highlighting the need for further process optimization to prevent hot tearing in high Mg and Cu content alloys.

Gao Q., Qiao G., Wang W., Ge Y., Ren J., Li W., Yang P., Lu X., Qiao J.

For precipitation-strengthened Al alloys, the interfacial segregation behavior of alloying elements plays an important role in controlling the effectiveness of precipitation strengthening.

Sun Q., Wang H., Yu S., Ma H., Zheng J., Hu Z.

To better achieve grain refinement and further optimize the comprehensive mechanical properties of Al-Zn-Mg-Cu-Zr alloys, this paper investigates the effect of trace Sc on the recrystallization behavior of Al-Zn-Mg-Cu-Zr alloys under isothermal multidirectional compression (IMC) and the mechanical properties in two-stage aging state. It was discovered that the addition of Sc enhanced the tensile and yield strengths of the alloys by 3.8% and 4.3%, respectively, and simultaneously increased the elongation from 13.4% to 15.4%. The OM, EBSD and TEM techniques were used to characterize the microstructure of the alloy. The results showed that the Al3(Sc,Zr) phase produced by the addition of 0.25% Sc not only refines the grains, but also changes the recrystallization behavior of the alloy by pinning the dislocations and (sub) grain boundaries in the combination of IMC deformation. It inhibits the generation of geometric dynamic recrystallization (GDRX) grains and the nucleation of discontinuous dynamic recrystallization (DDRX) grains but promotes the formation of continuous dynamic recrystallization (CDRX) as the predominant mode of dynamic recrystallization. The alloy gains a finer grain structure by simultaneously promoting the formation and inhibiting the growth of recrystallized grains. As a result, the improvement in the overall mechanical properties of Al-Zn-Mg-Cu-Sc-Zr alloys brought about by the addition of Sc can be attributed primarily to the refinement of the initial as-cast grains, as well as fine-grain strengthening due to the inhibition of recrystallized grain growth and the Orovan strengthening of the nanoscale secondary phase Al3(Sc,Zr) itself.

Su Z., Li X., Chen H., Xu S.

In this work, the microstructure and mechanical properties of the Al–5Cu–1Mn–0.3Ti alloy prepared by different casting processes were investigated. The results showed that direct squeeze casting can further refine the grain and θ-Al2Cu phase, which is favourable to the uniform distribution of the θ-Al2Cu phase. The fluffy θ-Al2Cu/α-Al interface was caused by the severe pressure loss during the indirect squeeze casting process. The strength and elongation of direct squeeze casting alloy are 508 MPa and 18.5%, which are 40.3% and 123% higher than those of the alloys of indirect squeeze casting. The in situ tensile experiments revealed that the crack initiation mechanism of the indirect squeeze casting alloy is the debonding of the θ-Al2Cu phase at the grain boundaries.

Li Q., Zhang X., Guo C., Qiao J.

In this paper, a one-step hot extrusion dual-stage solution treatment method is employed to fabricate high-strength and tough T-shaped complex cross-section 7055 (Al-Zn-Mg-Cu-Zr) alloy profiles, and a detailed investigation is conducted on the microstructure and mechanical properties. The results indicate that the comprehensive mechanical properties of the 7055 aluminum extruded alloy using the two-stage solution aging treatment are excellent. This is particularly evident in the balance between strength and ductility, where outstanding strength is accompanied by a plasticity that is maintained at 13.2%. During the extrusion process, the deformation textures are mainly composed of brass and copper, forming a 15.1% recrystallization texture Cube. In addition, the equilibrium phase η(MgZn2) precipitated in the grain is the main strengthening phase, and there are large discontinuous grain boundary precipitates at the grain boundary, which hinders the grain boundary dislocation movement and has great influence on the mechanical properties of alloy materials.

Zhao B., Xing S., Gao W., Yan G.

Squeeze casting process can effectively resolve the casting difficulties for wrought aluminum alloys by pressurized solidification. The effects of applied pressure (0.1–125 MPa) on the microstructure refinement, non-equilibrium eutectic phase aggregation and fracture behavior of Al-Zn-Mg-Cu alloys prepared by squeeze casting were investigated through metallography, scanning electron microscopy and energy dispersive spectroscopy. The results showed that the primary α-Al grains transformed from coarse dendrites to refined equiaxed grains with increasing pressure. Considerable primary refinement was achieved at 100 MPa, with a significant decrease by 63% in the average grain size from 273 µm to 101 µm; the non-equilibrium eutectic phases were homogenized and refined, and almost dissolved into the Al matrix after T6 heat treatment. The mechanism of solidification behaviors in pressurized solidification was elucidated. Firstly, the applied pressure increased the thermodynamic driving force to promote primary grain nucleation. Secondly, the solute diffusion and constitutional undercooling at the front of the solid/liquid interface front were inhibited by pressure, and grain growth in a dendritic structure was thus restrained. Thirdly, interdependence theory and thermodynamic calculations were conducted to quantitatively describe the primary grain size changes under pressurized solidification. Lastly, the ternary eutectic reaction L → α-Al + T-Mg (Al, Zn, Cu)2 + Al2Cu and binary eutectic reaction L→ α-Al + Al7Cu2Fe were suppressed by the reduced solute segregation. Furthermore, when the pressure increased from 0.1 MPa to 125 MPa, the ultimate tensile strength was raised from 428 MPa to 538 MPa, almost approaching that of samples by forging process. The refined eutectic phases decreased stress concentration and improved fracture behaviors.