半固态镁合金中液相的凝固方式及组织形貌

Solidification Modes and Morphology of Liquid Phase of Semi-solid Mg Alloy

采用快速液淬方法分析研究了AZ91D镁合金半固态液相的凝固方式和组织形貌,结果表明:镁合金半固态液相的凝固方式与冷却速度所决定的过冷度有重要关系。在液淬快冷的条件下,液相先析出α相,部分依附于初生固相晶粒结晶生长,部分在液相中独立形核生长。较大的过冷度使α相长成“毛刺状”或树枝晶状。共晶凝固按离异生长和共生生长两种方式进行,离异生长形成粗大的晶界β相,共生生长形成层片状组织。初生固相晶粒中形成的小液池,其凝固方式和结晶组织与晶间液相基本相同,但由于液相量少,共晶凝固主要以离异方式进行。

The solidification modes and morphology of liquid phase of semi-solid AZ91D Mg alloy by liquid quenching were investigated. The results indicated that the solidification modes of liquid phase of semi-solid Mg alloy were in close relationship with the degree of supercooling determined by cooling rate. Under conditions of liquid quenching, liquid phase precipitated a-phase firstly. Some a-phase clung to primary solid grains and grew up, others nucleated independently and grew up in the liquid phase. The big degree of supercooling caused that a-phase grew into spear-shape or dendrite. Eutectic solidification developed by divorced growth and coupled growth. Divorced growth generated bigger β-phase in grain boundaries. Coupled growth generated lamellar structures. The solidification modes and morphology of the small liquid bathes inside the primary solid grains were almost the same as that of the liquid phase between the grains. Due to smaller liquid phase, eutectic solidification modes of small liquid bathes developed by divorced growth mostly.