Influence of Heat Treatment on Precipitation Behavior and Mechanical Properties of Extruded AZ80 Magnesium Alloy

doi:10.1007/s40195-020-01094-0

Abstract

Abstract:

By means of annular channel angular extrusion technology and solution treatment, the AZ80 supersaturated solid solution was prepared. The β-Mg₁₇Al₁₂ precipitate morphologies analysis along with its sizes and area fraction measurement was performed to investigate mechanical properties variation of alloy at various aging temperature. The results indicated that after solution treatment, the intergranular precipitate of as-extruded alloy was re-dissolved into the matrix, effectively decreasing the stress concentration, which was beneficial to the enhancement of elongation. At aging temperatures of 300 °C, Widmanstatten structure, lath-shaped precipitate, and intergranular precipitate were observed, while at 175-200 °C, cellular structure and oval-shaped particle were also identified. The morphology, area fraction, size of the precipitates, and PFZs (precipitate free zones) width worked together to affect the age-hardening behavior of the alloy. The strength and hardness of the peak-aged samples decreased with the increase in aging temperature, which is primarily attributed to the reduction in cellular structure area fraction and the corresponding increase in the interlamellar spacing, and the coarsening of the rhombus precipitate.

Key words: AZ80 mg alloy, Annular channel angular extrusion, Heat treatment, Precipitate, Mechanical properties

Xi Zhao, Fa-Fa Yan, Zhi-Min Zhang, Peng-Cheng Gao, Shu-Chang Li. Influence of Heat Treatment on Precipitation Behavior and Mechanical Properties of Extruded AZ80 Magnesium Alloy[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(1): 54-64.

Figures/Tables 17

References 36

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Precipitate morphologies	Aging temperature (°C)
Widmanstatten structure	175-300
Lath-shaped precipitate	175-300
Intergranular precipitate	175-300
Cellular structure	175-250
Oval-shaped precipitate	175-250

Precipitate morphologies	Aging temperature (°C)
Widmanstatten structure	175-300
Lath-shaped precipitate	175-300
Intergranular precipitate	175-300
Cellular structure	175-250
Oval-shaped precipitate	175-250

	Continuous precipitates				Discontinuous precipitates				PFZ
Aging condition	Rhombus		Lath-shaped		Lamellar		Oval-shaped	Intergranular
Aging condition	Length	Width	Length	Width	Width	Spacing	Diameter	Diameter	Width
175 °C -30 h	0.30-0.70	0.07-0.20	0.20-1.50	0.08-0.15	0.10-1.00	0.24-0.45	0.10-0.30	0.30-0.80	0.04-0.06
200 °C -24 h	0.70-1.00	0.15-0.35	0.20-1.50	0.08-0.15	0.10-1.00	0.40-1.00	0.20-0.40	0.50-1.00	0.50-1.00
250 °C -18 h	0.80-1.20	0.20-0.40	0.20-3.00	0.08-0.15	0.30-1.50	0.60-1.50	0.20-0.40	0.70-2.00	1.20-2.50
300 °C -12 h	2.50-8.00	1.00-2.50	0.30-3.50	0.08-0.20	-	-	-	1.00-3.00	1.50-3.00

	Continuous precipitates				Discontinuous precipitates				PFZ
Aging condition	Rhombus		Lath-shaped		Lamellar		Oval-shaped	Intergranular
Aging condition	Length	Width	Length	Width	Width	Spacing	Diameter	Diameter	Width
175 °C -30 h	0.30-0.70	0.07-0.20	0.20-1.50	0.08-0.15	0.10-1.00	0.24-0.45	0.10-0.30	0.30-0.80	0.04-0.06
200 °C -24 h	0.70-1.00	0.15-0.35	0.20-1.50	0.08-0.15	0.10-1.00	0.40-1.00	0.20-0.40	0.50-1.00	0.50-1.00
250 °C -18 h	0.80-1.20	0.20-0.40	0.20-3.00	0.08-0.15	0.30-1.50	0.60-1.50	0.20-0.40	0.70-2.00	1.20-2.50
300 °C -12 h	2.50-8.00	1.00-2.50	0.30-3.50	0.08-0.20	-	-	-	1.00-3.00	1.50-3.00

Ageing schedule	Microstructural characteristics^a				Tensile properties^b
Ageing schedule	d (μm)	f_β (%)	f_DP (%)	f_CP (%)	UTS (MPa)	TYS (MPa)	El (%)
Homogenized	420.0(± 5.0)	-	-	-	206(± 8)	97(± 6)	10.7(± 1.1)
Extruded	23.7(± 2.5)	-	-	-	292(± 7)	165(± 4)	15.5(± 0.8)
T4	26.6(± 1.5)	0	0	0	267(± 4)	148(± 2)	19.1(± 0.5)
175 °C -30 h	27.4(± 1.5)	73.8(± 1.5)	48.0(± 1.5)	25.8(± 1.7)	327(± 13)	225(± 9)	11.6(± 1.2)
200 °C -24 h	28.6(± 1.8)	90.0(± 1.5)	33.7(± 1.8)	56.3(± 2.0)	306(± 10)	203(± 7)	10.7(± 1.3)
250 °C -18 h	29.1(± 2.0)	78.4(± 2.0)	21.4(± 2.0)	57.0(± 2.2)	297(± 8)	185(± 5)	11.7(± 0.9)
300 °C -12 h	29.3(± 2.0)	54.8(± 2.5)	0	54.8(± 2.5)	279(± 7)	176(± 5)	13.5(± 0.7)