Microstructure And Properties Of Wrought Al-15.5Si-4.5Cu-1.0Zn-0.7Mg-0.5Ni Alloy

With the social development in recent years, the engine power was increased gradually, which on the strength of the piston alloy at high temperature strength in particular, have higher requirements. Hypereutectic Al-Si alloy are widely used in automotive applications, particularly in piston industry, because of excellent wear resistance, corrosion resistance, high specific strength, low coefficient of thermal expansion and good dimensional stability.The experimental alloy is Al-15.5Si-4.5Cu-lZn-0.7Mg-0.5Ni-0.3Zr-0.2V-0.1Ti. By DC casting, hot deformed and T6heat treatment, the study obtains a new type hypereutectic Al-Si alloy with outstanding mechanical properties at room and high temperature. According to a series of experiments and analysis, such main conclusions are as followed:(1) The microstructure of the DC casting alloy consists of α-Al dendrites, primary silicon, eutectic silicon, Al2Cu(θ), Al7Cu4Ni(γ), Al2(Si,Mg,Zr,Fe,Ni,Cu), Al9(Cu,Fe)Ni, Al5Cu2Mg8Si6phase and so on. The average size of primary silicon particles on edge,1/2radius, and the central region of alloy ingot are respectively15μm,15μm,18μm.(2) Hot deformation eliminates the defects formed in cast alloys. The fracture of primary Si particles resulted in the degradation of room-temperature and high-temperature mechanical properties. Alloys after T6heat treatment, primary silicon angular passivation of crystalline,eutectic silicones granulate significantly, Al2Cu(θ) phase content decreased, Al2(Si,Mg,Zr,Fe,Ni,Cu),Al2(Mg,Si,Cu) phases disappeared while a dispersively distributed phase A15Cu2Mg8Si6precipitating from matrix.(3) The ultimate tensile strength of DC casting alloys is280MPa, tensile strength after heat treatment for16h(solution treatment at500℃for4hours, aging treatment at150℃) the maximum is393MPa, increased by40%compared to cast alloy. Strength of the hot deformed alloy after heat treatment is349MPa.(4) The tensile strength at300℃of DC cast alloys is163MPa. The tensile strength is140Mpa after heat treatment and decreased by14%, but the elongation was increased by12%. The tensile strength of deformed alloy after the T6heat treatment is121MPa, dropped by 25%compared to the cast, while the elongation rate is14.20%.(5) Fractographic studies indicate that the fracture of alloys is in the hybrid mode. The strengthening mechanisms of alloys are grain refinement, solid-solution, precipitation strengthening and excess phase strengthening and so on.