热处理对Mg­3Sn­1Y合金显微组织及显微硬度的影响

摘要

在电阻炉中采用熔剂保护熔铸Mg­3Sn­1Y(质量分数，%)合金，并通过Olympus GX71光学显微镜(OM)、装备能谱(EDS)的FEI QUANTA 400型扫描电镜(SEM)、RigakuD/max­3C型X射线衍射(XRD)、TUKON2100维氏型硬度计和CRY−2P型DTA差热分析仪等分析合金的铸态组织、固溶及时效热处理对组织和时效硬化的影响。结果表明，Mg­3Sn­1Y 合金铸态组织由α­Mg 枝晶、枝晶间断续网状 Mg2Sn 相和弥散分布的细小颗粒及短棒状MgSnY相组成。固溶处理后Mg2Sn相已完全固溶，而具有高温稳定性的MgSnY相依然分布在基体中。加入Y元素可以提高合金的高温稳定性。Mg­3Sn­1Y合金具有典型的时效硬化特征，时效温度提高，一定程度上有利于时效峰出现；但时效温度过高，基体组织的长大会降低析出强化作用，延缓峰值硬度的出现。%A nominal composition of Mg­3Sn­1Y (mass fraction,%) magnesium alloy was prepared by casting with flux protection in electric­resistance furnace. The microstructures as­cast, solution treatment and aging hardening of the Mg­3Sn­1Y alloy by different aging treatments after solution treatment were investigated by an Olympus GX71 optical microscope (OM), an FEI QUANTA 400 scanning electron microscope (SEM) equipped with an energy­dispersive X­ray spectroscop (EDS), a RigakuD/max­3C X­ray diffraction (XRD), a TUKON2100 Vickers hardness tester and a CRY−2P differential thermal analyzer (DTA). The results show that as­cast Mg­3Sn­1Y alloy consists of dendritic α­Mg and intermittent mesh inter­dendrite boundaries Mg2Sn phase, the dispersion tiny particles and fine rod­shaped MgSnY phase. After the solution treatment, the Mg2Sn phase is completely redissolved, and the MgSnY phase with the high temperature stability still distributes in the matrix. The addition of yttrium elements can improve the high temperature stability of Mg­Sn alloy. Mg­3Sn­1Y alloy exhibits obvious aging hardening characteristics. The increase of the aging temperature is advantageous to the occurrence of aging hardening peak to some extent. On the contrary, grain growth of the matrix will decrease the function of separation and strengthening and delay the appearance of aging hardening peak as the ageing temperature is too high.