Micro-alloying And Short Heat Treatment Process Of Al-Si Casting Alloy Research

Al-Si alloy has been widely used in key parts such as wheel hub and sub-frame of automobile due to its excellent comprehensive properties.However,with the continuous improvement of social demand,the strength of the general Al-Si alloy is low,and the heat treatment process time takes too long,it has become a research hotspot to achieve rapid heat treatment and ensure good mechanical properties at the same time in aluminum alloy field.This dissertation based on casting Al-7Si,by adding alloying elements Er,Cu,and Mg compound modification,by OM,SEM,TEM,Brinell hardness tester,Universal testing machine and other methods studies the composite micro-alloying on the reinforcement mechanism and the microstructure,hardness and tensile properties change rule during the process of short heat treatment of aluminum alloy.The results show that:The element Er can not only refine the grain of Al-Si-Cu-Mg alloy but also play an important role in modifying eutectic silicon.After Er modification,the dendritic density of the alloy increases and the growth trend is obvious.The eutectic silicon changes from large blocks to fine fibrous.The increase of Cu content in the alloy can improve the hardness and strength,but lose some plasticity.When the Cu content reaches 1.0 wt.%,the hardness and tensile strengths are 76.2 HBS and 237.3 MPa,respectively,and the elongation is reduced to 3.7%.During the solution treatment,the eutectic silicon of Al-7Si-1Cu-0.3Mg alloy has gone through the process of crushing,spheroidizing and coarsening.The size of eutectic silicon increases with the prolonging of solution time,while the aspect ratio decreases.When the solution temperature is increased from 540?to 550?,the spheroidization rate of eutectic silicon is accelerated.After solution treatment at 550?for 60 min,the Er phase in the alloy changes from long strip to coral-like.Besides,the long needle-like Al₅Fe Si phase is passivated after solution treatment.The higher the temperature of solution treatment,the higher the diffusion coefficient and the faster the diffusion of alloying elements.When the alloy is treated at 550?,the solubility rate of Cu and Mg elements into Al matrix is faster and more uniform.The short heat treatment process of Al-7Si-1Cu-0.3Mg alloy is as follows:solution treatment at 550?for 180 min,aging treatment at 170?for 4 h.Er can restrain the nucleation temperature of Al matrix and eutectic silicon,and reduce the melting temperature of eutectic silicon to 570.4?.The hardness of the alloy increases first and then decreases with aging time.At 170?,the aging hardening rate reaches the maximum,and the hardness of the alloy reaches the peak value of 109.6 HBS after aging for 4 h.After short heat treatment,the tensile strength and elongation of the alloy are 330.1MPa and 8.6%,respectively.The tensile fracture mode is a mixed fracture,and the primary crack originates in the eutectic zone.