Effect Of Modification And Heat Treatment On The Microstructure And Properities Of AL-SI Alloys

Al-Si alloy is an important casting alloy, which has low density, high strength,thermal expansion coefficient, good thermal stability, wear resistance and so on.Currently, Al-Si alloy is widely used in automobiles, motorcycles and othermanufacturing industries. In this paper, The effect of complex modification and T6heat treatment on microstructure and properties of ADC12alloy and R14alloywere studied and find a better modification process parameters.The experimental results showed that：Add0.6%Al-5Ti-B master alloy onADC12alloy refinement, The α-Al dendrite size and secondary dendrite armspacing of ADC12alloy were minimum with the addition of0.6%Al-5Ti-B masteralloy. The best modification effect of eutectic silicon particles in ADC12alloy canbe obtained with the addition of0.60%RE, long needle-like eutectic silicon wererefined into short rod-like or granular shape. The ADC12alloy with the additionsof0.6%Al-5Ti-B and0.60%RE have the optimal microstructure, α-Al andeutectic Si have been well refined. With the T6heat treatment, eutectic silicon rodlength is decreased, and converd into the near-spherical particles.The optimal refinement effect of primary silicon is obtained when R14alloycontains0.08%P, primary silicon crystals were signifcantly refned from coarsepolygonal shape to fne blocky shape with smooth edges and corners, and theaverage size of primary silicon is decreased from64.4μm to27.7μm. RE canchange both of primary silicon and eutectic silicon, while the addition is0.8%, theaverage size of primary silicon were30.2μm, and eutectic silicon phases weremodifed from needle-like structure to short rod-like and discrete particles. TheR14alloys with the additions of0.08%P and0.60%RE have the optimalmicrostructure, both of primary silicon and eutectic silicon. With the T6heattreatment, primary silicon were converd into the near-spherical particles.With the composite modification and T6heat treatment, the room temperaturetensile properties, hardness and wear resistance of ADC12alloy were improved.The tensile strength, elongation and Brinell hardness of unmodified ADC12alloywere183MPa,1.02%,70HB, respectively. The tensile strength, elongation andBrinell hardness of composite modified ADC12alloy were273MPa,3.59%,85HB,respectively. ADC12alloy with T6heat treatment, the tensile strength and Brinellhardness were253MPa and104HB, respectively.With the composite modification and T6heat treatment, the room temperaturetensile properties, hardness and wear resistance of R14alloy were improved significantly. The tensile strength, elongation and Brinell hardness of unmodifiedR14alloy were212MPa,0.71%,102HB, respectively. The tensile strength,elongation and Brinell hardness of composite modified R14alloy were271MPa,2.34%,120HB, respectively. R14alloy with T6heat treatment, the tensile strengthand Brinell hardness were374MPa and160HB, respectively.