等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。

Microstructure and mechanical properties of ultrafine grained Mg15Al alloy processed by equal-channel angular pressing

An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing (ECAP) through a die with an angle of φ=90° at 553K following route Bc.The microstructure and fracture morphology were investigated with Optical microscope,SEM,TEM and mechanical properties were measured.It was found that the network-like β-Mg17Al12 phases in as-cast Mg15Al alloy are broken into small blocky and dispersed uniformly with increasing pressing passes.Moreover,many nano-sized Mg17Al12 particles precipitate in the ultrafine α-Mg matrix.The grains are refined obviously and distribute randomly in the grain orientation.However,grain refinement is inhomogeneous in different area of alloy.The average size of primary phase α-Mg is reduced to about ～1μm while the grains of around 100nm are obtained in some local two-phase area.With additional ECAP passes up to 8 passes,coarsening of grain occurs by dynamic recovery.The room temperature tensile test and hardness test results showed that the mechanical properties of Mg15Al alloy enhance remarkably after 4 passes ECAP.The hardness is increased by 32.04%.The ultimate tensile strength and elongation to failure increase from 150MPa to 269.3MPa and 0.05% to 7.4%,respectively.Comparing with pressing 4 passes,the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 passes ECAP.Fracture morphology of the ECAPed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows brittle cleavage fracture.