Microstructures And Mechanical Properties Of Die-Cast Al-Si-Cu-(Er) Alloys

Because of their higher specific strength and corrosion resistance, good foundry and processing properties as well as excellent electric and thermal conductivity, die-cast aluminum alloys have found a wide application in aeronautical and automotive industries. And thus, the systematic research concerning the microstructure and property of die-cast aluminum alloys is of both important theoretical referring value and practical directing significance.In this investigation, the pure Al, Si and Cu are chosen as the raw material. Through melting, the die casting Al-Si-Cu-(Er) alloys have been fabricated.The microstructures, tensile properties and low-cycle fatigue properties of the die-cast Al-Si-Cu-Er alloys are studied, and compared with the die casting Al-Si-Cu alloy.Microstructural observations show that the die-cast Al-Si-Cu-Er alloy poss much finer microstructure than the die-cast Al-Si-Cu alloy. And the formation of the needle-like eutectic Si phase gets inhibited, while the globule-like eutectic Si phase can be obtained.The tensile experimental results show that compared with the die casting Al-Si-Cu alloy, the ultimate tensile strength of the die-cast Al-Si-Cu-Er alloy at room temperature increases by 25%, the yield strength by 16%, and the elongation to fracture at room temperature,150℃and 200℃increases by 49%,58%and 70%, respectively.The results of low-cyclic fatigue tests show that the die casting Al-Si-Cu-(Er) alloys exhibit the cyclic strain hardening and cyclic stability, mainly depending on the imposed total strain amplitude. For the Al-Si-Cu-(Er) alloys, the relation between plastic and elastic strain amplitudes as well as reversals to failure can be described by Coffin-Manson and Basquin equations, respectively. In addition, a linear relation between tensile hysteresis energy and fatigue life can be noted.The fractographic results reveal that under tensile loading conditions, the die-cast Al-Si-Cu-(Er) alloys mainly exhibit the ductile fracture feature, while under low-cycle fatigue loading conditions, the cracks of the Al-Si-Cu-(Er) alloy with different processing states initiate transgranularly at the surface of fatigue samples and propagate in a transgranular mode.