Improving the Mechanical Properties of Mg-Gd-Y-Ag-Zr Alloy via Pre-Strain and Two-Stage Ageing

doi:10.1007/s40195-022-01485-5

Abstract

Abstract:

In this study, we investigated the effects of single-stage ageing (SSA), two-stage ageing (TSA), 2% pre-strain + single-stage ageing (P2%SSA) and 2% pre-strain + two-stage ageing (P2%TSA) on the mechanical properties of as-extruded Mg–8Gd–3Y–0.5Ag–0.5Zr alloy (E alloy). Compared with the SSA treatment, the TSA treatment increased the number density of $\beta ^{\prime}$ phase. The P2%SSA and P2%TSA treatments generated the $\gamma ^{\prime}$ phase and chain-like precipitates in addition to the $\beta ^{\prime}$ phase. The contributions of these ageing treatments to the alloy strengthening can be ranked as P2%TSA > P2%SSA > TSA > SSA, because the increments in the tensile yield strength were estimated to be 199 MPa > 148 MPa > 144 MPa > 110 MPa. Different from the traditional strengthening of $\beta ^{\prime}$ phase in the E + SSA and E + TSA alloys, the composite precipitates comprising the $\beta ^{\prime}$ phase, $\gamma ^{\prime}$ phase and chain-like precipitates in the E + P2%SSA and E + P2%TSA alloys provided better combined strengthening effect. The $\beta ^{\prime}$ phase was still dominated in the strengthening effect of the composite precipitates. Owing to the higher number density of $\beta ^{\prime}$ phase in the composite precipitates, the E + P2%TSA alloy exhibited the better mechanical performance as compared with the E + P2%SSA alloy. Finally, the E + P2%TSA alloy had the ultimate tensile strength of 452 MPa, the tensile yield strength of 401 MPa and elongation to failure of 3.3%.

Key words: Magnesium alloys, Rare earth, Age hardening, Pre-strain, Mechanical properties

Baotian Du, Zijian Yu, Kang Shi, Ke Liu, Shubo Li, Wenbo Du. Improving the Mechanical Properties of Mg-Gd-Y-Ag-Zr Alloy via Pre-Strain and Two-Stage Ageing[J]. Acta Metallurgica Sinica (English Letters), 2023, 36(3): 456-468.

Figures/Tables 13

Table 1 Chemical composition of the Mg-8Gd-3Y-0.5Ag-0.5Zr alloy (wt%)

Gd	Y	Ag	Zr	Mg
8.0	2.9	0.4	0.1	Bal

Fig. 1 Age-hardening curves of GW83K + 0.5Ag alloy under different ageing conditions: a single-stage ageing and 2% pre-strain + single-stage ageing at 200 °C; b two-stage ageing (first-stage ageing (pre-ageing) at 100 °C/12 h + second-stage ageing at 200 °C) and 2% pre-strain + two-stage ageing. Notes E refers to as-extruded, E + P2% refers to as-extruded + 2%pre-strain

Fig. 2 Tensile stress-strain curves of GW83K + 0.5Ag alloy under as-extruded and peak-aged conditions at room temperature

Table 2 Summary of tensile properties of as-extruded and peak-aged GW83K + 0.5Ag alloy at room temperature

Condition	TYS (MPa)	UTS (MPa)	EL (%)
E	202	304	22.8
E + SSA	312	412	4.3
E + TSA	346	435	4.7
E + P2%SSA	350	445	4.3
E + P2%TSA	401	452	3.3

Fig. 3 Microstructure of GW83K + 0.5Ag alloy in different states: a as-cast alloy; b solution treated alloy; c as-extruded alloy

Fig. 4 EBSD results of a, c, e E alloy and b, d, f E + P2% alloy: a, b EBSD inverse pole figure (IPF) maps; c, d twin maps; e, f local misorientation maps

Fig. 5 Average angle distribution of local misorientation of GW83K + 0.5Ag alloy: a, c E alloy; b, d E + P2% alloy; a, b whole gains; c, d DRXed grains

Fig. 6 BF-TEM images of E + P2% alloy showing a the tensile twin and b, c dislocations in two-beam conditions

Fig. 7 IPFs of whole grains, deformed grains and DRXed grains: a, b, c E alloy; e, f, g E + P2% alloy

Fig. 8 HAADF-STEM results of the E + SSA alloy: a, b the electron beam is parallel to$\left[ {0001} \right]_{\alpha }$; c, d the electron beam is parallel to $[11\overline{2} 0]_{\alpha }$

Fig. 9 HAADF-STEM results of the E + TSA alloy: a, b the electron beam is parallel to $\left[ {0001} \right]_{\alpha }$; c, d the electron beam is parallel to $[11\overline{2} 0]_{\alpha }$

Fig. 10 HAADF-STEM results of the E + P2%SSA alloy: a, b the electron beam is parallel to $\left[ {0001} \right]_{\alpha }$; c, d the electron beam is parallel to $[11\overline{2} 0]_{\alpha }$

Fig. 11 HAADF-STEM results of the E + P2%TSA alloy: a, b the electron beam is parallel to $\left[ {0001} \right]_{\alpha }$; c, d the electron beam is parallel to $[11\overline{2} 0]_{\alpha }$

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