Effect Of Aging And Si On Precipitated Phase And Mechanical Properties Of Cast Al-5Cu Alloy

Al-Cu alloy is an important kind of high toughness casting alloy,which is widely used,but casting defects such as porosity,segregation and hot cracking will reduce the yield and increase the production cost.The research shows that Si element can reduce the hot cracking tendency and improve the mechanical properties,and the influence of trace elements onα-Al/θ′interface is a hot academic research topic,and the research of interface engineering is an important guarantee for understanding and regulating the precipitated phases.In this paper,SEM,XRD,TEM,hardness test and tensile test were used to study the effects of Si and aging heat treatment process on the precipitated phases and mechanical properties of cast Al-5Cu alloy.The main results are as follows:（1）Si element is beneficial to improve the mechanical properties of as-cast Al-5Cu alloy.The analysis of as-cast structure and tensile fracture surface shows that the main reason for improving as-cast mechanical properties is that Si changes the morphology and distribution of eutectic structure at grain boundaries.By analyzing the residual Al₂Cu phase in the solid solution structure,the grain boundary segregation is serious,and the solid solution effect is worse.（2）At 510℃×6h+170℃,the tensile strength and elongation of Al-5Cu-（0,0.6）Si alloy increase firstly and then decrease with the aging time increasing（1-20h）.At the early stage of aging（1-7h）,Al-5Cu-0.6Si alloy has higher elongation and tensile strength than Al-5Cu alloy.In the late aging period（11-20h）,the decline rate of tensile strength of Al-5Cu-0.6Si alloy is slower than that of Al-5Cu alloy.（3）After aging at 170℃for 1h,θ’size of precipitated phase in Al-5Cu-0.6Si alloy is larger than that in Al-5Cu alloy.At the early aging stage（1-7h）,Al-5Cu-0.6Si alloy has higher elongation and tensile strength than Al-5Cu alloy.（4）There are large second phases（Al₂Cu and Al₃Cu）in the grain boundary and in the crystal,leading to the presence of precipitation-free zone（PFZ）near the phase,which impedes the uniformity of precipitation dispersion in the matrix.（5）After aging for more than 7 hours,the precipitated phases in the matrix grow obviously,and the quantity and density decrease.There is growth competition between adjacent precipitated phases.In addition,a continuous step precipitation zone appears in the crystal.