热轧及再结晶退火对Mg-8Al-3.5Sr镁合金晶粒细化的影响

Effect of hot rolling and recrystallization annealing on grain refinement of Mg-8Al-3.5Sr magnesium alloy

目前关于耐热镁合金的塑性变形及变形后的热处理工艺的基础研究相对较少,然而这又是镁工业发展的瓶颈,本文对铸态耐热Mg-8Al-3.5Sr镁合金固溶处理后进行不同压下量的热轧以及再结晶退火研究,利用光学显微镜和扫描电子显微镜研究试样的金相显微组织。研究结果表明:合金试样经380℃×24h固溶处理后显微组织内出现棒状Al4Sr相,晶界变得清晰可见且呈多边形化,平均晶粒尺寸为65μm;随热轧压下量的增加,平均晶粒尺寸呈下降趋势,压下量为80%时得到最佳显微组织,平均晶粒尺寸为26μm,当压下量继续增加到90%时,晶内出现大量裂纹;将该合金在300℃条件下保温1h,获得了等轴再结晶组织,平均晶粒尺寸进一步下降到21.5μm。再结晶退火温度过高时,晶粒呈现异常长大状态,同时会析出大量点状Mg17Al12相。

At present,basic research on the plastic deformation of the heat-resistant magnesium alloy and the subsquent heat treatment process is relatively little.However,they are the bottleneck of the magnesium industry.Therefore,the as-cast Mg-8Al-3.5Sr magnesium alloy was subjected to solution treatment,and then hot rolling and recrystallization annealing.The microstructure of the samples before and after annealing was studied by optical microscope and scanning electron microscope.The results show that the rod-like Al4Sr phase is appeared,and the grain boundaries become clearly visible as polygonal with an average grain size of65μm,when the alloy sample was treated by solution at380℃for24h.With the increase of hot rolling reduction,the average grain size decreased,and the optimum microstructure which had an average grain size of26μm was obtained when the hot rolling reduction was80%.When the reduction amount was increased to90%,there were a large number of cracks.When the recrystallization annealing condition was300℃for1h,the equiaxed recrystallization structure appeared in the crystal,and the average grain size was further reduced to21.5μm.When the recrystallization annealing temperature was too high,the grains would grow abnormally and the Mg17Al12phase precipitated.