冷速与固溶工艺对含SiC的镁合金晶界β相形成的影响

Effects of Cooling Rate and Solid Solution Process on Grain Boundary β Phase in Magnesium Alloy Containing SiC

采用铜模喷铸与等温固溶相结合,对比研究不同冷速和固溶工艺对AZ91+1SiC合金晶界β相的形貌及体积分数的影响,并对其形成规律进行分析。结果表明,相比于炉冷合金,铜模喷铸的高冷速可以显著细化晶粒,形成过饱和固溶体,溶质偏析程度的减弱有利于抑制β相的形成。随铜模内径减小,非平衡凝固效应的增强导致β相含量进一步降低,其中内径为2mm时的β相体积分数仅为4.3%,相比内径8mm的合金减少66.1%。经320℃固溶处理,内径为8mm的快冷合金中β相体积分数由保温2h时的9.1%降至4h时的5.5%。继续延长到8h后,β相含量无明显变化。随固溶温度升高,快冷合金中β相含量显著降低,其中400℃保温2h后β相基本消失,最终形成完全固溶组织。

Effects of cooling rate and isothermal solid solution process on the morphology and volume fraction of grain boundary β phase in AZ91+1 SiC alloy were investigated by copper mould spray casting and subsequent isothermal solid solution to reveal its formation mechansim.The results show that the high cooling rate of spray casting can refine the grain size significantly in comparison with furnace cooling.The formation of supersaturated solid solution can reduce the solute segregation degree,which is beneficial to inhibiting the formation of β phase.With the decrease of inner diameter,the enhanced non-equilibrium effect leads to the further decrease of β phase.The volume fraction ofβphase with diameter of 2 mm is only 4.3%,reduced by 66.1% than that of ones with 8 mm in diameter.After isothermal treatment at 320 ℃ for 2 h,the volume fraction of β phase in quenched alloy with diameter of 8 mm is decreased to 9.1%.As the increase of holding time,its value is further reduced to 5.5% for 4 hand varied sliGHTly after 8 h.The amount ofβphase is decreased greatly with solid solution temperature increase,where a complete solution structure can be obserevd after holding at 400℃ for 2 hdue to the disappearance of β phase.