Microstructure characteristics and solidification behavior of thixomolded Mg-9%Al-1%Zn alloy

• Published in: Transactions of Nonferrous Metals Society of China 2011-02, Vol.21 (2), p.250-256
• Main Authors: ZHANG, You-fa, LIU, Yong-bing, CAO, Zhan-yi
• Format: Article
• Language: English
• Subjects: Agglomeration; Heating; Instability; Liquid alloys; Magnesium base alloys; Microstructure; Morphology; solid particle; Solidification; solidification behavior; Supercooling; thixomolded AZ91D alloy; Transformations
• ISSN: 1003-6326
• DOI: 10.1016/S1003-6326(11)60706-1

Experimental investigation and theoretical analysis of the microstructure of thixomolded AZ91D were carried out to comprehensively understand the morphology transformation of solid particles and the solidification behavior. Typical microstructure of thixomolded AZ91D is composed of α-Mg and β-Mg 17Al 12, characterized with α un, α prim and eutectic. Four kinds of α un are classified according to the morphology and generation mechanism, such as spherical (α 1), irregular (α 2), entrapping liquid alloy inside (α 3) and entrapping pool inside (α 4). Under the effect of heating, shearing, collision, agglomeration or fragmentation, α 2 and α 4 can be the middle states of α 1 and α 3. Similarly, α 4 and α 3 can also break into α 2 and become α 1 at the end. Controlled by undercooling, α prim nucleates and spherically grows within the remaining liquid alloy of thixomolded AZ91D until instability growth. The investigated microstructure was theoretically proved according to the analysis of Mg-Al binary phase diagram.