Effect Of Sr Addition And Minor Cu On Microstructure And Mechanical Properties Of A357 Alloy

The A357 alloy is studied in this paper. The effect of adding quantity of Sr element on the structure and mechanical properties of the A357 alloy have been investigated. The optimized addition of Sr element is obtained. On the base this paper reseaches effect of Cu addition on the structure and mechanical properties of the A357 alloy. And the optimized heat-treated agent is obtained by orthogonal experiment.The experimental results show that: with the increase of Sr addition, the morphology of the eutectic Si changes from pine+plane to fibrics shape, and the size of the eutectic Si fiber becomes much finer, and the microstructure of eutectic Si are gradually evenly distributed. At the same time, with the increase of Sr addition, the compound Sr in the alloy increase. Sr modifier is sensitive on the cooling rate. At as-cast state, the effect of Sr modification on the tensile strength and elongation is the same. That is at first increased and then lowered with the increase of Sr content. When Sr content is 0.04%, the mechanical properties of as-cast A357 alloy are highest. The tensile strengh is increased 8.64MPa compared with unmodified and the elongation rises 50%.With the increase of minor Cu element, the hardness gradually increased. When the Cu element is 0.2%, the hardness is improved to 28% compared with the A357 alloy without Cu element. And the increase in yield strength is also obvious. When Cu element is 0.2%, the yield strength is increased about 20MPa, and improved to 20% compared with the alloy without Cu element. The influence ranking of the alloy heat-treated parameters can be obtained by orthogonal experimental method as following: solution time, solution temperatue, aging time, aging temperature. The optimized heat-treated parameter is solution temperatue 541℃, solution time 12h, aging temperature 170℃, aging time 10h. The mechanical property obtained isσb=344.53MPa,σ0.2=287.50MPa,δ=4.34%, is increased 13.91MPa and 23.04MPa compared with the strength of alloy not containing Cu element by respectively, but the elongation decreases.