Of High Strength And High Toughness Malleable Cast Al-si-cu-mg Alloy

In this paper, the microstructure and mechanical properties of Al-Si-Cu-Mg casting alloy have been investigated by employing the metallgraphic analysis SEM analysis and DSC analysis, and the effect of Bi on microstructure and mechanical properties of casting and wrought Al-Si-Cu-Mg alloy have been studied, too.And the mechanism has been dicussed.Firstly, hot extrusion was carried out in Al-Si-Cu-Mg casting alloy samples and the effect of hot extrusion on the microstructure and mechanical properties of this alloy was studied. The results show that the hot extrusion improves as-cast microstructure, spheroidizes grains of eutectic Si; hot extrusion can markedly improve the mechanical properties of this alloy, especially ductility. Owing to hot extrusion, the tensile-strength and elongation percentage of this alloy without heat treatment increases by 26.8% and 212.5% respectively. It is also shown that T6 heat-treatment techniques play an important pole in mechanical properties of Al-Si-Cu-Mg wrought alloy. Experiments confirm that the optimal T6 heat-treatment technique is 520℃× 10h+200℃×10h, and then the alloy has optimal mechanical properties, the tensile strength, extensilbility and hardness are 401.7MPa 4.9% and 136-141HBS, respectively, and the tensile strength, extensilbility and hardness are increased by 36.1%, 1200% and 27.3%, compared with the mechanical properties of Al-Si-Cu-Mg casting alloy treated by T6 heat-treatment.Secondly, Bi was added to casting and wrought Al-Si-Cu-Mg alloy, and the influence of Bi on the microstructure and mechanical proerties of the alloy was studied. The results show that Bi has markedly modifying effect on Al-Si-Cu-Mg casting alloy; It occurs that the modi faction of eutectic Si from flake to fibrous and grain refinement of primary α-Al; compared with unmodified alloy, the casting tensile-strength and elongation percentage of the alloy with 3% Bi added are enhanced by 3.9% and 62.5% respectively. The results also show that Bi can markedly improve the microstructure of Al-Si-Cu-Mg wrought alloy.Finally, It is compared that the mechanical proerty between casting and wrought Al-Si-Cu-Mg alloy and Al casting alloy ZL108 or Al wrought alloy 4032. It is discovered that, compared with ZL108, the tensile strength of as-cast Al-Si-Cu-Mg casting alloy is increased by 5.1%, and extensibility is enhanced from 0.2% to 3.2%; and the tensile strength of Al-Si-Cu-Mg casting alloy treated byT6 heat-treatment is 15.7%, and extensibility is enhanced from 0.2% to 0.5%. And it is found that, compared with 4032, the tensile strength of Al-Si-Cu-Mg wrought alloy treated byT6 heat-treatment is increased by 7.4%, extensibility is enhanced from 0.2% to 6.5%, and hardness is increased by 16.7%.