铜模激冷SiCp/AZ91镁合金晶粒细化及固溶组织演化

Grain Refinement of Copper-mould Quenched SiCp/AZ91 Magnesium Alloy and Subsequent Microstructure Evolution during Isothermal Solid Solution Treatment

摘要:

采用SiC颗粒添加与铜模喷铸相结合，提高快冷条件下熔体的异质形核潜力，制备出亚快速凝固镁合金细晶组织，在此基础上对比研究了热处理温度（320℃、370℃和400℃）对晶界离异共晶β-Mg17Al12相动态固溶过程的影响。结果表明，亚快速凝固AZ91+1wt%SiC合金经320℃+2h处理后固溶不完全，仍然保留原始不规则花瓣状组织，少量基体相中出现细小条纹。370℃+2h时晶界消失速率加快，同时存在少量晶界残留区域。400℃+2h处理后可得到单相α-Mg固溶体，组织为细小多边形等轴晶。添加2wt%SiC后，激冷合金的细化效果提高，高温原子扩散距离缩短，有利于固溶过程进行。SiC的添加及组织的细化使得铜模喷铸镁合金显微硬度值提高28.75%，固溶处理后晶界相的消失导致合金硬度值下降。

Abstract:

With the addition of SiC particle and copper-mould spray casting, the heterogeneous nucleation ability of AZ91 magnesium alloy is enhanced under high cooing condition and thus the grain refinement of sub-rapid solidified microstructure was fabricated. Then, the effect of annealing temperature (320℃、370℃ and 400℃) on the dynamic solid solution process of divorce eutectic β-Mg17Al12 phase was investigated. As for the spray casted AZ91+1wt%SiC after annealing for 320℃+2h, incomplete solid solution occurs, accompanied by the preservation of initial irregular petal-like morphology and the formation of tiny fringes. After annealing at 370℃, the disappearing rate of β phase is accelerated except for the residual of few grain boundary region. With further increasing temperature to 400℃, a single solid solution of α-Mg phase forms and its morphology transits into fine polygonal grain. Grain refinement is more obvious after the addition of 2wt%SiC, which promotes the process of solid solution due to the shortened atomic diffusion distance. The hardness of copper-mould spray casted magnesium alloy is enhanced by 28.75% due to the addition of SiC and increase of grain refinement, whereas a decline trend appears after solid solution treatment because of the reduction of grain boundary.