不同Mg、Si质量比对压铸铝合金组织与性能的影响

Influence of Varied Mg/Si Mass Ratio on the Microstructure and Mechanical Properties of Aluminum Die Casting Alloys

研究了Mg、Si质量比对Al-4Mg-xSi-0.6Cr合金组织和性能的影响。结果表明,未加入Si时,Mg主要固溶于α-Al基体中,少量形成颗粒状的Al_3Mg_2相,综合力学性能好。随着Si的加入,Mg主要与Si形成Al-Mg_2Si共晶组织,合金强度显著提高,但是塑性急剧下降。Mg、Si元素质量比减小导致Al-Mg_2Si共晶组织层片间距增大,形貌变为带有尖端的凹多边形,容易在拉伸过程中形成应力集中,加速合金断裂。当Mg、Si质量比减小到1.6时,继续提高Si含量,Mg_2Si相的数量不再增加,但是有长条状共晶Si生成,强化合金的同时使合金的塑性进一步降低。含Cr相的种类和形貌与Mg、Si元素质量比有关,过剩Mg时Cr元素以大块状Al13Cr2相存在,过剩Si时Cr元素以不规则状Al5(Cr,Fe)Si相均匀分布。

The influence of w（Mg）/w（Si）mass ratio on the microstructure and mechanical properties of Al-4 Mg-xSi-0.6 Cr die casting alloys was investigated.The results reveal that Mg is mainly soluted inα-Al matrix and a small amount of Al3Mg2 particle phase can be generated,which results in the high comprehensive mechanical properties withoutSi added in the alloy.With the addition ofSi elements,the strength of the alloy is increased,while ductility is decreased sharply due to Mg andSi formed Al-Mg2Si eutectic microstructure.Al-Mg2Si eutectic lamellar spacing is increased and it＇s morphology is transferred into concave polygon with the decrease of Mg/Si mass ratio,which can accelerate fracture during tensile process as a result of stress concentration.When the Mg/Si mass ratio is decrease to 1.6,with the increase ofSi,the amount of Mg2Si phase keeps constant value.Meanwhile,the strength is increased and ductility is decreased due to long stripSi eutectic phase formed in the die casting alloy.The category and morphology of Cr phase are related with Mg/Si mass ratio.With excess of Mg,the Cr exists in form of large block Al13 Cr2 phase,while with excessSi,the Cr is distributed evenly with irregular Al5（Cr,Fe）Si.