Effect of Al on Expansion Behavior of Mg-Al Alloys During Solidification

doi:10.1007/s40195-018-0780-y

Abstract

Abstract:

The cooling curves and the change of contraction/expansion during solidification and cooling were tested by using a self-made device which could achieve the one-dimensional contraction instead of three-dimensional contraction of the casting. Then, the effects of Al content (0, 1.1, 3, 5, 10, 12.9, 15, 17, 19, 22, 24 and 30 wt%) on the thermal contraction/expansion of the binary Mg-Al as-cast alloys during solidification were obtained. The results showed that expanding instead of contraction was present in Mg-Al alloys with the addition of 0-30 wt% Al during solidification. The values of expansion significantly increased at first and then decreased with the increase in Al content. And the maximum expansion ratio of 0.44% (maximum expansion value: 0.841 mm) was present in the Mg-15 wt% Al alloy. Contraction instead of expansion occurred once the temperature drops to the temperature corresponding to the expansion value in total, indicating the occurrence of a continuous expansion during the solidification process in mushy zone for the Mg alloys with Al addition of 5-30 wt%. The expansion value in total consisted of two parts: the expansions occurring in the liquid-phase zone and mushy zone. The expansion in liquid zone was present in every Mg-Al alloy, and it contributed to the most proportion of the total expansion value when the Al content in Mg-Al alloy was lower than 10 wt% or higher than 22 wt%. However, the total expansion value was mainly determined by the solidification behavior in mushy zone when the Al content was among 10-22 wt% in Mg-Al alloys.

Key words: Solidification, Mg alloys, Al content, Expansion

Yi Meng, Jian Sun, Lei-Gang Cao, Yue Yang, Hai-Tao Zhang, Jian-Zhong Cui. Effect of Al on Expansion Behavior of Mg-Al Alloys During Solidification[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(5): 559-565.

Figures/Tables 6

Fig. 1 Schematic diagram of displacement tested module

Fig. 2 Curves of time-temperature (t-T), time-displacement (t-l) of Mg-Al alloys with different Al contents: a 0 wt%; b 1 wt%; c 3 wt%; d 5 wt%; e 10 wt%; f 12.9 wt%; g 15 wt%; h 17 wt%; i 19 wt%; j 22 wt%; k 24 wt%;l 30 wt%

Fig. 3 a Max expansion, b liquidus temperatures, solidus temperatures and corresponding temperatures of max expansion, c expansion displacement measured between liquidus temperature and corresponding temperature of max expansion of Mg-Al alloys with different Al contents during solidification

Table 1 Highest temperature in cavity, max expansion values (L), the corresponding expansion displacements between liquidus temperatures and TL (Δl), and their expansion displacements in liquid-phase zone (L - Δl) for Mg-Al alloys with different Al contents during solidification

Al content (wt%)	3	5	10	12.9	15	17	19	22	24	30
Highest temperature (°C)	658.6	682.5	668	657.1	663.9	650.9	662	658	610.4	661.3
L (mm)	0.045	0.069	0.254	0.706	0.841	0.452	0.200	0.072	0.100	0.084
Δl (mm)	0.001	0.004	0.140	0.644	0.730	0.366	0.161	0.050	0.024	0.005
L - Δl (mm)	0.044	0.065	0.114	0.062	0.111	0.086	0.039	0.022	0.076	0.079

Fig. 4 XRD patterns of as-cast Mg-Al alloys with different Al addition

Fig. 5 SEM microstructures of Mg-Al alloys with different Al contents: a 5 wt%; b 10 wt%; c 15 wt%; d 19 wt%

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