研究了几种主要合金化元素Fe、Mn、Zn以及稀土元素Ce在AlMg4.5和A1Mg4.5Si2.6压铸合金中的存在形式,比较了显微组织中第二相种类和形貌对合金力学性能的影响.结果表明AlMg4.5Si2.6压铸合金中主要存在α-Al相、多边形状Al8(Fe,Mn)2Si相、层片状Al-Mg2Si共晶相和短棒状Al(Si)Ce相,AlMg4.5压铸合金中主要存在α-Al相、少量Al-Al3Mg2共晶相、长条状A16(Fe,Mn)相以及不规则的小块状Al4Ce相,微量Zn主要固溶于合金基体中.在两种合金金相组织中都有剪切带的存在,溶质原子在该区域富集,第二相含量更高.相比于AlMg4.5合金,AlMg4.5Si2.6合金强度和硬度更高,但是塑性较低.AlMg4.5Si2.6合金中层片结构的Al-Mg2Si共晶组织在拉伸过程中容易形成解理台阶,表现为明显的脆性断裂.AlMg4.5压铸合金在拉伸过程中表现为穿晶断裂和沿晶断裂的混合断裂机制,长条状的Al6(Fe,Mn)粒子尖端处很容易造成应力集中,加速了合金的断裂.
The existence form of the main alloy elements of Fe,Mn,Zn and Ce and the effect of different category and morphology of secondary phase on the microstructure and mechanical properties have been investigated in the AlMg4.5 and AlMg4.5Si2.6 die casting alloys.The results reveal that α-Al phase,Al8 (Fe,Mn)2Si phase,Al-Mg2Si lamellar eutectic phase and short rod-like Al (Si) Ce phase existed in A1Mg4.5Si2.6 die casting alloy.Al-Al3Mg2 pseudo-eutectic phase,elongated Al6(Fe,Mn) phase and irregular small Al4Ce phase were mainly found in AlMg4.5 die casting alloys,all trace elements of Zn were dissolved in α-Al matrix of two alloy.Meanwhile,the shear band,where solute atoms were enriched and secondary phase content was higher,were found in both alloys.Compared with AlMg4.5 alloy,AlMg4.5Si2.6 alloy had higher strength and hardness,but lower elongation.AlMg4.5Si2.6 alloy showed obvious brittle fracture due to the lamellar Al-Mg2Si eutectic phase was easy to form cleavage step during tensile process.However,AlMg4.5 die casting alloy showed a mixed fracture mechanism oftransgranular and intergranular fracture in the tensile test,the stress concentration at the tips of the elongated A16 (Fe,Mn) particles can accelerate the fracture of the alloy.