Role of Grain Boundary Segregation and Nanoprecipitation on the Tensile Properties and Thermal Stability of Dilute Mg-0.7Al-0.3Ca (wt%) Alloy

doi:10.1007/s40195-025-01929-8

Abstract

Abstract:

A dilute Mg-0.7Al-0.3Ca (AX0703, wt%) alloy with high strength is developed via conventional low-temperature extrusion, with tensile yield strength of 376 MPa and elongation of 5.3%. As-extruded AX0703 sample exhibits the bimodal grain structures consisting of dynamically recrystallized (DRXed) ultrafine grains and coarse non-DRXed grains with strong basal texture, which contributes to the strength. The numerous nano-Al₂Ca phases were developed in non-DRXed grains during extrusion, which not only generates the remarkable precipitation hardening effect, but also favors the improved thermal stability by retarding recrystallization process. Also, it is found that co-segregations of Al-Ca solutes at DRXed grain boundaries hinder grain growth during heat treatment at 300 °C, contributing to the thermal stability of as-extruded AX0703 alloy. This work provides valuable insights into the development of high-strength and low-alloyed Mg extrusions with high thermostability.

Key words: Mg-Al-Ca alloy, Microstructure, Mechanical properties, Thermal stability, Grain boundary segregation

Xiaoqing Liu, Xiaoguang Qiao, Xiaoye Qiu, Xianke Zhang, Chubin Yang, Dongdong Zhang, Xiurong Zhu, Mingyi Zheng. Role of Grain Boundary Segregation and Nanoprecipitation on the Tensile Properties and Thermal Stability of Dilute Mg-0.7Al-0.3Ca (wt%) Alloy[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(12): 2165-2178.

Figures/Tables 12

Fig. 1 a OM and b SEM images of the as-cast AX0703 alloy; elemental distribution of c Al, d Ca

Fig. 2 a Band contrast image, b IPF map, c IPF image of as-extruded AX0703 alloy; d TEM DF image of DRXed regions in the as-extruded AX0703 alloy; e, f, g TEM BF images of non-DRXed regions in the as-extruded alloy; HRTEM images corresponding to the h phase A, i phase B in g

Fig. 3 a Elemental distribution of Mg, Ca and Al atoms in the APT tip, b the corresponding concentration depth profiles detected perpendicular to the recrystallized grain boundary ROI 1, c the corresponding concentration depth profiles detected across the interface ROI 2 of Al-Ca nanoprecipitate

Fig. 4 IPF maps of dilute AX0703 extrusion alloy under different annealing times: a 300 °C-10 min, b 300 °C-20 min, c 300 °C-30 min, d 300 °C-60 min, e 300 °C-120 min, f 300 °C-300 min, g 300 °C-600 min, h 300 °C-1200 min

Fig. 5 IPFs of the dilute AX0703 extrusion alloy under different annealing times: a 300 °C-10 min, b 300 °C-20 min, c 300 °C-30 min, d 300 °C-60 min, e 300 °C-120 min, f 300 °C-300 min, g 300 °C-600 min, h 300 °C-1200 min

Fig. 6 TEM microstructure of the dilute AX0703 extrusion alloy annealed at 300 °C-10 min and 300 °C-600 min: a TEM BF micrograph and SAED pattern of the AX0703 alloy annealed at 300 °C-10 min; b TEM BF micrograph corresponding to the yellow rectangular region in a; c HRTEM figure corresponding to the yellow rectangular region in b; d HAADF-STEM image of the AX0703 alloy annealed at 300 °C-600 min; elemental mappings of e Al and f Ca

Fig. 7 a IPF map of as-extruded Mg-1Al alloy; IPF maps of the as-extruded Mg-1Al alloy under different annealing times: b 300 °C-10 min, c 300 °C-60 min, d 300 °C-1200 min

Fig. 8 a IPF of as-extruded Mg-1Al alloy; IPFs of the as-extruded Mg-1Al alloy under different annealing times: b 300 °C-10 min, c 300 °C-60 min, d 300 °C-1200 min

Fig. 9 a Tensile engineering stress-strain curves of as-extruded and as-annealed AX0703 alloys, b plot map of engineering stress and elongation to failure for Mg-Al-Ca ternary alloys[[21,22,23,24]]

Table 1 Tensile properties of as-extruded and as-annealed AX0703 and Mg-1Al alloys under the same annealing conditions

Samples		YS (MPa)	UTS (MPa)	Elongation (%)	Grain size (μm)
As-extruded and as-annealed AX0703 alloys	As-extruded	376 ± 6.2	387 ± 7.3	5.3 ± 2.1	0.65 ± 0.1
	300 °C-10 min	356 ± 5.9	366 ± 5.7	6.9 ± 1.9	0.85 ± 0.1
	300 °C-20 min	307 ± 3.7	311 ± 4.0	24.5 ± 2.3	1.4 ± 0.2
	300 °C-30 min	258 ± 3.6	295 ± 4.1	27.9 ± 3.2	1.8 ± 0.2
	300 °C-60 min	188 ± 3.3	218 ± 3.5	27.4 ± 3.4	2.5 ± 0.3
	300 °C-120 min	156 ± 2.1	214 ± 3.3	27.4 ± 3.3	3.3 ± 0.4
	300 °C-300 min	137 ± 2.2	194 ± 3.2	31.2 ± 3.9	4.0 ± 0.5
	300 °C-600 min	117 ± 1.9	196 ± 2.2	33.5 ± 4.3	4.9 ± 0.8
	300 °C-1200 min	100 ± 1.4	163 ± 1.8	32.9 ± 4.3	6.1 ± 1.1
As-extruded and as-annealed Mg-1Al alloys	As-extruded	272 ± 4.2	320 ± 5.1	12.3 ± 1.5	0.7 ± 0.1
	300 °C-10 min	161 ± 3.0	236 ± 3.8	27.4 ± 3.0	2.6 ± 0.2
	300 °C-20 min	152 ± 2.5	229 ± 3.6	29.7 ± 4.1	3.2 ± 0.3
	300 °C-30 min	136 ± 2.0	211 ± 3.0	27.4 ± 4.1	3.6 ± 0.4
	300 °C-60 min	126 ± 2.0	194 ± 2.9	21.3 ± 3.9	4.2 ± 0.4
	300 °C-120 min	118 ± 1.9	183 ± 2.6	32.4 ± 4.3	5.3 ± 0.8
	300 °C-300 min	107 ± 1.5	170 ± 2.5	32.6 ± 4.7	6.8 ± 1.0
	300 °C-600 min	101 ± 1.5	167 ± 2.6	32.9 ± 4.6	8.3 ± 1.2
	300 °C-1200 min	94 ± 1.3	152 ± 1.8	27.5 ± 4.0	9.5 ± 1.4

Table 2 Strengthening contributions from σ0, GBs, Orowan precipitations, dislocations and texture of the AX0703 extrusion alloy

Alloy	Regions	σ_GB (MPa)	σ_dislo (MPa)	σ_tex (MPa)	σ0 (MPa)	σ_Orowan (MPa)	Predicted strength (MPa)
AXM070304	DRXed	228	43	-	19	61	351 (86 vol.%)	348
AXM070304	Non-DRXed	-	82	171	19	58	330 (14 vol.%)	348

Fig. 10 Functional relationship between (Dn-D0n) and t of AX0703 alloy: a n = 1, b n = 2, c n = 3, d n = 4; the functional relationship between (Dn-D0n) and t of Mg-1Al alloy: e n = 1, f n = 2, g n = 3

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