Improving mechanical properties of age-hardenable Mg-6Zn-4Al-1Sn alloy processed by double-aging treatment

doi:10.1016/j.jmst.2017.07.021

Abstract

Abstract:

Microstructure and mechanical properties of a new high-strength Mg-6Zn-4Al-1Sn alloy were investigated. Microstructure of the as-cast Mg alloy exhibited partially divorced characteristics. The dendritic structure of the Mg-6Zn-4Al alloy was significantly refined with the addition of 1% (in weight) Sn, but Mg₂Sn phases were not formed. In addition, an icosahedral quasi-crystal phase was formed in the as-cast Mg-6Zn-4Al-1Sn alloy. It was found that after the double-aging treatment through two different heat treatments on the Mg-6Zn-4Al-1Sn alloy, the precipitates were finer and far more densely dispersed in the matrix compared with single-aged counterpart, resulting in a significant improvement in tensile strength with yield strength, ultimate tensile strength and elongation of 175 MPa, 335 MPa and 11%, respectively.

Key words: Magnesium alloy, Mg-Zn-Al-Sn, Double-aging treatment, Mechanical properties

Zhu treatmentShaozhen, Luo Tianjiao, Yang Yuansheng. Improving mechanical properties of age-hardenable Mg-6Zn-4Al-1Sn alloy processed by double-aging treatment[J]. J. Mater. Sci. Technol., 2017, 33(11): 1249-1254.

Figures/Tables 11

Table 1 Actual compositions (wt%) of the investigated alloys.

Alloy designation	Nominal composition	Zn	Al	Sn	Mn	Mg
ZA64	Mg-6Zn-4Al	5.6	3.86	-	-	Bal.
ZAT641.	Mg-6Zn-4Al-1Sn	5.6	3.85	0.96	-	Bal.
AZ91	Mg-9Zn-1Al	8.60	0.52	-	0.17	Bal.

Fig. 1. (a) SEM images of the as-cast ZAT641 alloy, (b) and (c) the magnified visions of A and B in (a).

Fig. 2. (a) SEM images of the as-cast ZAT641 alloy, (b) and (c) the magnified visions of A and B in (a).

Fig. 3. Back-scattered electronic image (a) and EPMA element distribution of (b) Zn, (c) Al, (d) Sn in the as-cast ZAT641 alloy.

Fig. 4. XRD pattern of as-cast ZAT641 alloy.

Fig. 5. Bright field images of divorced eutectic phase (a) and eutectic phase (c) in the as-cast ZAT641 alloy, (b) and (d) the corresponding SAED patterns. The insets in (a) and (c) are corresponding EDX results.

Fig. 6. Optical images of the as-aged ZAT641 alloy with different heat treatments: (a) single-aging, and (b) double-aging.

Fig. 7. Bright field TEM micrographs of ZAT641 alloy by different heat treatments taken along [11-20] Mg axis zone: (a) single-aging and (b) double-aging.

Fig. 8. Representative stress-strain curves of the as-aged alloys after different heat treatments collected at room temperature.

Table 2 Mechanical properties of the as-aged alloys.

Alloys	State	YS (MPa)	UTS (MPa)	Elongation (%)
ZAT641	Single-aging	144	294	8
ZAT641	Double-aging	175	335	11
AZ91	Single-aging	156	237	4

Fig. 9. Work-hardening rate as a function of true strain of the as-aged alloys.

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