The Study Of High Strength And Toughness Al-Si-Cu-Mg Cast Alloys On Microstructures And Mechanical Properties

Al-Si-Cu-Mg cast alloy is a traditional metal material with low density, light weight, good abrasion resistance and perfect flow property.With the requiring of energy conservation reduction and the environment protection,this alloy can be used for large volume parts with complicated structure in the aviation, spaceflight, automobile to replace iron parts.However, the mechanical properties of the traditional Al-Si-Cu-Mg alloys can not meet the needs of safety use of automotive key components, especially the weight-bearing parts.To improve the mechanical properties of traditional Al-Si-Cu-Mg cast alloy,three methods are applied in this paper.The effects of the alloying elements contents under different heat treatment,the addition of modificator Al-Sr and refiner Al-Ti-B,the electromagnetic stirring process are studied separately.Firstly,to study the interaction of the alloying elements contents under cast condition and after T4,T6 heat treatment,Al-(5,6,7) wt%Si-(1,2,3) wt%Cu-(0.3,0.6,0.9) wt%Mg test alloys were studied in this paper with orthogonal analysis.The results show that Al-6Si-3Cu-0.3Mg alloy has a better comprehensive mechanical property after T6 heat treatment than other alloys.The UTS is 382.01Mpa and the El is 3.82%.Secondly,the content of Al-5Sr modificator is adjusted in the alloy liquid.The morphology of eutectic silicon turns from thick strips to tiny fibrous organizations with 0.04%Sr content.And the eutectic silicon can be perfectly spheroidized after T6 heat treatment.The polygon Al2Si2Sr of 2～5μm compound will produce among grain boundary place with too much addition of Sr,which will have a negative impact on the mechanical property of the alloy.The 0.15% content of Ti can refine a-Al grains effectively with the addition of refiner Al-4Ti-B.Lastly,the effects of mechanical properties with 0/10/20A electromagnetic stirring process in different pouring temperatures during 760～605℃ were studied with a particular instrument. The fracture morphology of the alloy shows that the expansion of the crack always along the Low melting eutectic phase. With the elevation of pouring temperature,the dendrites’length of primary α-Al phase will increase,which is not good for the mechanical property.Better comprehensive mechanical property will be acquired with 20A electromagnetic stirring process and pouring in 685℃.The The UTS is 392.53MPa and the EI is 3.91%.