Microstructure and Mechanical Properties of Yb-Containing AZ80 Cast Alloys

doi:10.1007/s40195-025-01835-z

Abstract

Abstract:

The microstructural evolution and mechanical properties of Mg-8.0Al-xYb-0.5Zn (wt%, x = 0, 1, 2) cast alloys were investigated. With increasing Yb content, a significant grain refinement was observed, accompanied by the continuous refinement and fragmentation of the initial β-Mg₁₇Al₁₂ phase network. Concurrently, the Al₃Yb phase formed and coarsened. Calculations including formation enthalpy and lattice misfit, confirm that the Al₃Yb phase, which nucleates prior to the α-Mg and β-Mg₁₇Al₁₂ phases and exhibits a low lattice misfit with their low-index planes, serves as an effective heterogeneous nucleation site, significantly contributing to the observed microstructural refinement. Furthermore, Yb addition fundamentally suppresses constitutional supercooling by consuming Al atoms, which possess a high growth restriction factor, for the formation of Al-Yb phases. Subsequent tensile testing reveals that Yb solute promotes the generation of extension twins and the accumulation of dislocations during deformation, leading to a marked enhancement in the work-hardening capacity of the Yb-containing alloys. Benefiting from the refined microstructure and enhanced work hardening, the Mg-8.0Al-1.0Yb-0.5Zn alloy exhibits a favorable balance between mechanical strength and ductility, achieving an ultimate tensile strength of ~ 249.8 MPa and an elongation of ~ 11.70%, respectively.

Key words: Mg-Al-Yb-Zn cast alloys, Microstructure, Mechanical properties, Grain refinement

Qi Zhou, Yufeng Xia, Yu Duan, Baihao Zhang, Yuqiu Ye, Peitao Guo, Lu Li. Microstructure and Mechanical Properties of Yb-Containing AZ80 Cast Alloys[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(7): 1095-1108.

Figures/Tables 19

Table 1 Actual chemical compositions of the as-cast alloys

Alloys	Al	Zn	Yb	Mg
AZ80	7.93	0.55	-	Bal.
AYbZ810	8.12	0.52	0.95	Bal.
AYbZ820	7.89	0.49	2.11	Bal.

Fig. 1 Schematic diagram of the experimental process

Fig. 2 Backscattered electron (BSE) micrographs of as-cast AZ80-xYb alloys: a x = 0 wt%, b x = 1 wt%, c x = 2 wt%, d-f corresponding local magnification of the selected zones in a-c, g-i corresponding energy dispersive spectrometer (EDS) mapping images of d-f

Fig. 3 X-ray diffraction patterns of as-cast AZ80-xYb alloys

Table 2 EDS results of as-cast AZ80-xYb alloys (at.%) from Fig. 2

Site	Phase designation	Mg	Al	Zn	Yb
A	β-Mg₁₇Al₁₂	58.89	37.66	3.45	-
B	Al₃Yb	49.93	37.43	0.51	12.13
C	Al₃Yb	50.63	37.25	0.97	11.15
D	β-Mg₁₇Al₁₂	64.31	33.50	2.18	0.00
E	Al₃Yb	28.70	53.96	0.31	17.03
F	Al₃Yb	24.32	56.23	0.33	19.11
G	β-Mg₁₇Al₁₂	63.86	33.53	2.46	0.14

Fig. 4 Average size of β-Mg17Al12 and Al3Yb of as-cast AZ80-xYb alloys

Fig. 5 Orientation patterns of as-cast AZ80-xYb alloys: a x = 0 wt%, b x = 1 wt%, c x = 2 wt%. davg indicating the average grain size

Fig. 6 a Tensile stress-strain curves, b comparisons of the strength and ductility of different as-cast Mg alloys

Table 3 Ultimate tensile strength (σUTS), yield strength (σ0.2), elongation to fracture (EL), work hardening capacity (HC), and work hardening exponent (n) of the as-cast AZ80-xYb alloys

Sample	σ_UTS (MPa)	σ_0.2 (MPa)	EL (%)	H_C	n
AZ80	168.1 ± 5.2	133 ± 4.9	4.90 ± 0.5	0.402	0.287
AYbZ810	249.8 ± 4.8	149 ± 5.1	11.70 ± 0.3	1.001	0.336
AYbZ820	226.5 ± 5.5	135 ± 5.3	10.90 ± 0.6	0.946	0.327

Fig. 7 Fracture morphology of AZ80-xYb alloys at room temperature: a x = 0, b x = 1, c x = 2

Fig. 8 Work hardening curves for as-cast samples: a θ-ε, b θ-(σ-σ0.2)

Fig. 9 a, b Initial and fractured inverse pole figure (IPF) maps of AZ80, c, d initial and fractured IPF maps of AYbZ810, e, f initial and fractured special boundaries maps and corresponding misorientation angle distribution of AZ80, g, h initial and fractured special boundaries maps and corresponding misorientation angle distribution of AYbZ810, i, j initial and fractured KAM maps of AZ80, k, l initial and fractured KAM maps of AYbZ810

Table 4 Parameters in the Miedema model

Element	${\varphi }$	${n}^\frac{1}{3}$	${{{V}}}^\frac{2}{3}$	${{\mu}}$
Mg	3.45	1.17	5.81	0.10
Al	4.20	1.39	4.64	0.07
Yb	3.22	1.23	6.86	0.07

Fig. 10 Enthalpy of heat formation of binary compounds in AZ80-xYb alloys

Table 5 Crystal surfaces mismatch between α-Mg and Al3Yb

Crystal planes	Mg(0001)‖Al₃Yb(001)			Mg(0001)‖Al₃Yb(110)			Mg(0001)‖Al₃Yb(111)
Mg(hkil)	[$\overline{1 } 2 \overline{1 } 0$]	[$1 \overline{1 }0$ 0]	[$\overline{2 } 1 1$ 0]	[$\overline{1 } 2 \overline{1 } 0$]	[$\overline{2 } 1 1 0$]	[$\overline{1 }0 1 0$]	[$\overline{1 } 1 1 0$]	[$\overline{1 } 3 1 0$]	[$\overline{1 } 2 \overline{1 } 0$]
Al₃Yb(hkl)	[0 1 0]	[1 $\overline{1 }$ 0]	[1 0 0]	[0 0 1]	[1 $\overline{1 }$ 1]	[1 $\overline{1 } 0$]	[$\overline{1 }$ 0 $1$]	[$\overline{2 } 1 1$]	[$\overline{1 } 1 0$]
${d}_{\text{Mg}}$ (Å)	5.525	5.525	3.190	5.525	8.439	6.379	5.525	9.568	5.525
${d}_{\text{Al3Yb}}$ (Å)	4.278	6.050	4.278	4.278	7.410	6.050	6.050	10.479	6.050
θ (°)	0	15	0	0	5.26	0	0	0	0
δ (%)	20.82			13.43			9.51

Table 6 Crystal surfaces mismatch between β-Mg17Al12 with Al3Yb

Crystal planes	Mg₁₇Al₁₂(001)‖Al₃Yb(001)			Mg₁₇Al₁₂(001)‖Al₃Yb(110)			Mg₁₇Al₁₂(001)‖Al₃Yb(111)
Mg₁₇Al₁₂(hkl)	[1 0 0]	[1 1 0]	[0 1 0]	[1 0 0]	[9 5 0]	[0 1 0]	[9 5 0]	[5 9 0]	[0 1 0]
Al₃Yb(hkl)	[1 0 0]	[1 1 0]	[0 1 0]	[1 1 0]	[1 1 1]	[0 0 1]	[1 0 1]	[2 1 1]	[1 1 0]
${d}_{\text{Mg}17\text{Al}12}$ (Å)	10.526	14.885	10.526	10.526	7.754	10.526	7.754	7.754	10.526
${d}_{\text{Al}3\text{Yb}}$ (Å)	8.556	12.100	8.556	12.100	7.410	12.100	6.050	10.479	12.100
θ (°)	0	0	0	0	6.2	0	0.9	1	0
δ (%)	18.71			11.63			24.02

Fig. 11 Crystallographic matching relationship of α-Mg with Al3Yb

Fig. 12 Crystallographic matching relationship of β-Mg17Al12 and Al3Yb

Figure 9 Relationship between (σ-σ0.2)θ and (σ-σ0.2) for as-cast AZ80-xYb alloys

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