High Strength and Heat Resistance of Low-RE-Containing Mg Alloy Achieved via Substantial Dynamic Precipitates

doi:10.1007/s40195-024-01751-8

Abstract

Abstract:

Conventional high-strength Mg-RE-based wrought alloys usually contain a high amount of RE solutes, which largely increases the alloy cost and thus restricts their adoptions. In this work, we developed a low-RE-containing Mg-3Sm-1Nd-0.6Zn-0.4Zr alloy by hot extrusion with low extrusion ratio, which shows a high tensile yield strength (TYS) of 435 MPa and a satisfactory elongation of 5.6% at room temperature, outperforming most Mg-Gd-Y-based extrusion alloys with RE contents of 12 wt% at least. Outstanding high-temperature strength, such as the TYS of 280 MPa at 200 °C and 251 MPa at 250 °C, is also obtained in this alloy. The alloy presented a typical bimodal grain structure including coarse hot-worked grains with a strong texture and fine recrystallized grains with random orientations. Also, abundant Mg₃RE particles were mostly introduced in hot-worked grains and at recrystallized grain boundaries by dynamic precipitation during extrusion. Consequently, the high strength of this alloy is principally attributed to the combined hardening effect of numerous Mg₃RE particles, fine recrystallized grains, and strongly textural hot-worked grains, rather than the ultra-strong age-hardening effect in traditional high RE-alloyed Mg alloys.

Key words: High strength, Mg-RE alloys, Dynamic precipitation, Heat resistance

Dongdong Zhang, Mingyang Chen, Xiaoru Zhang, Ke Li, Liqing Wang, Zhanyong Zhao, Peikang Bai, Daqing Fang. High Strength and Heat Resistance of Low-RE-Containing Mg Alloy Achieved via Substantial Dynamic Precipitates[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(11): 1830-1842.

Figures/Tables 9

Fig. 1 a Age-hardening curves of as-extruded sample at 200 °C; b tensile curves of as-extruded and as-aged samples under various temperatures

Table 1 Comparison of mechanical properties of the studied alloy and other typical Mg-RE extrusion alloys after T5 treatment

Alloys	Temperature (ºC)	UTS (MPa)	TYS (MPa)	EL (%)
Mg-3Sm-1Nd-0.6Zn-0.4Zr	443 ± 2.1	435 ± 2.6	5.6 ± 0.55	443 ± 2.1
	300 ± 4.4	280 ± 4.3	8.0 ± 1.31	300 ± 4.4
	278 ± 4.8	251 ± 5.2	13.2 ± 1.52	278 ± 4.8
WE54 (Mg-5Y-4RE-0.5Zr) [31]	25	331	300	−
	200	266	246	−
	250	196	126	−
Mg₉₇Y₂Cu₁, at.% [32] (Mg-6.84Y-2.45Cu)	25	337	297	8.1
Mg₉₇Y₂Cu₁, at.% [32] (Mg-6.84Y-2.45Cu)	200	344	273	16.3
Mg-8.4Gd-4.4Li-3.5Y-1.4Zn [33]	25	39	295	2.5
Mg-8.4Gd-4.4Li-3.5Y-1.4Zn [33]	200	279	143	19.8
Mg-11Gd-4.5Y-1Nd-1.5Zn-0.5Zr [34]	25	473	373	4.1
	200	405	343	4.2
	250	369	316	6.3
Mg-8Gd-2Y-1Nd-0.3Zn-0.6Zr [35]	25	271	143	18.7
Mg-8Gd-2Y-1Nd-0.3Zn-0.6Zr [35]	200	233	134	20.1
Mg-8.2Gd-3.8Y-1Zn-0.4Zr [36]	25	470	395	8
Mg-8.2Gd-3.8Y-1Zn-0.4Zr [36]	250	399	328	13
Mg-10Gd-3Y-0.5Zr [37]	25	339	312	4.0
	200	362	253	15.5
	250	308	190	33.0

Fig. 2 a OM image of as-homogenized sample, b OM image, c IPF map, d GOS map, and e-g IPFs and e1-g1 PFs of different regions of as-extruded sample

Fig. 3 SF maps and corresponding distribution histograms for various slip systems: a, d basal < a > slip, b, e prismatic < a > slip, and c, f pyramidal < c + a > slip

Fig. 4 a, b Backscattered SEM images and c, d bright-field TEM images of as-extruded sample

Fig. 5 Bright-field TEM images along with the associated SAED patterns of three typical particles

Fig. 6 HAADF image, TEM image and HR-TEM image of dynamic precipitates in recrystallized and hot-worked grains: a-c hot-worked grain, d inverse FFT image of phase boundary, e, f one recrystallized grain

Fig. 7 a Grain boundary misorientation maps, b, c bright-field TEM image of a high density of LAGBs in hot-worked grains, d KAM map, e, f bright-field TEM image under two-beam conditions of dislocation substructures in hot-worked grains

Fig. 8 Microstructures of as-aged sample: a, b bright-field TEM images showing a heat stability of recrystallized grains and residual dislocations, c bright-field TEM image of ageing-induced precipitates in hot-worked grains, d SAED pattern, and e, f HR-TEM images along with FFT patterns of precipitates

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