Microstructure, Mechanical Properties and Texture Evolution of Mg-Al-Zn-La-Gd-Y Magnesium Alloy by Hot Extrusion and Multi-Pass Rolling

doi:10.1007/s40195-020-01062-8

Abstract

Abstract:

A high-ductility Mg-8.10Al-0.42Zn-0.51Mn-1.52La-1.10Gd-0.86Y (wt%) alloy was developed by hot extrusion and multi-rolling processes. Relationships between microstructure, mechanical properties and texture evolution of the extruded and rolled alloy were investigated. The rolling process had significant effect on grain refinement of the extruded plate. The grain size reduced from 12.3 to 4.9 μm with the increasing rolling pass. With the increase in rolling pass, the proportion of dynamic recrystallized (DRXed) grains increases due to particle-stimulated nucleation, grain boundary nucleation and twin induced nucleation. In the process of multiple rolling, the basal pole gradually tilted from normal direction to transverse direction due to the asymmetric deformation and irregular grain deformation, resulting in the weakening of the base texture. The results showed that grain refinement and texture weakening were the main reasons for the good ductility of the alloy.

Key words: Extrusion, Multi-rolling, Grain refinement, Texture evolution, Mechanical properties

Qiyu Liao, Wenxin Hu, Qichi Le, Xingrui Chen, Ke Hu, Chunlong Cheng, Chenglu Hu. Microstructure, Mechanical Properties and Texture Evolution of Mg-Al-Zn-La-Gd-Y Magnesium Alloy by Hot Extrusion and Multi-Pass Rolling[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(10): 1359-1368.

Figures/Tables 14

Table 1 Chemical composition (wt%) of the modified AZ80 magnesium alloy

Al	Zn	Mn	La	Gd	Y	Mg
8.10	0.42	0.51	1.52	1.10	0.86	Bal.

Table 2 Rolling conditions and rolling parameter of the extrusion plates

Pass	Rolling direction	Temperature (K)	Thickness change (mm)	Thickness reduction (%)
0	-	603 ± 5	?300- 300 × 20	Primary extrusion
1	\|\|ED	623 ± 5	20-17.3	13.5
2	\|\|ED	623 ± 5	20-17.3-13.4	13.5 + 22.5
3	\|\|ED	623 ± 5	20-17.3-13.4-10.2	13.5 + 22.5 + 23.6
4	\|\|ED	623 ± 5	20-17.3-13.4-10.2-8.3	13.5 + 22.5 + 23.6 + 20.9

Fig. 1 Process flow diagram of the hot extrusion plate and multi-pass hot rolling sheets

Fig. 2 Microstructure characteristics of the extruded sample of the alloy (ED-ND plane): a optical morphology map; b IPF (inverse pole figure) map; c average grain size versus area fraction distributions map and the black curve means lognormal fitting of the grain size distributions; d grain misorientation distribution map; (dAVG: the diameter of average grain size; SD: standard deviation of grain size)

Fig. 3 Microstructure characteristics of the alloy after the multi-rolling processes: a-d IPF maps; e-h grain misorientation distribution maps; i-l average grain size vs area fraction distribution maps and the black curve means lognormal fitting of the grain size distributions

Fig. 4 {0001}, {$10 \bar{1} 0$} and {$1 \bar{2} 10$} pole figures of the extruded and rolled samples: a the original extruded sample; b the rolled (pass 1) sample; c the rolled (pass 2) sample; d the rolled (pass 3) sample; e the rolled (pass 4) sample

Fig. 5 Schematic diagram of grain rotation in the selected plane (ED/RD-ND plane)

Fig. 6 Engineering stress-strain carves of the extruded and rolled samples along the RD

Table 3 Summarized mechanical properties of the AZ80RE Mg alloy sheets

Sample	UTS (MPa)	YS (MPa)	EL (%)
As-extruded	269.7 ± 2.2	141.5 ± 1.6	10.2 ± 1.2
As-rolled (pass 1)	291.7 ± 1.5	177.7 ± 2.1	15.6 ± 0.9
As-rolled (pass 2)	311.5 ± 1.1	179.2 ± 1.8	18.8 ± 1.1
As-rolled (pass 3)	311.2 ± 2.0	193.9 ± 1.7	21.4 ± 0.8
As-rolled (pass 4)	312.8 ± 1.6	196.3 ± 1.6	25.5 ± 0.8

Fig. 7 TEM micrographs of nucleation characteristics of DRXed grains of the 4th rolled sample: a dislocation around the particle; b dislocation tangle in the grain boundaries; c high-density dislocations in the grain; d fine grains in the confluence of twins; e DRX nucleation in the twins

Fig. 8 Different types of grain of the sheets a as-extruded; b as-rolled (pass 1); c as-rolled (pass 2); d as-rolled (pass 3); e as-rolled (pass 4): blue—recrystallized grains, yellow—substructures, red—deformed grains; f-j frequency of the different types of grains shown in a-e, respectively

Fig. 9 UTS and YS are plotted against the d-1/2 for the extruded and rolled AZ80RE alloy

Fig. 10 Quantitative analysis of (0001)/< $11\bar{2}0$ > basal ship Schmid factor (SF) of the multi-rolling samples: a, e as-rolled (pass 1); b, f as-rolled (pass 2); c, g as-rolled (pass 3); d, h as-rolled (pass 4)

Fig. 11 Variations failure elongation of the AZ80RE alloy sheets during extrusion and multi-rolling processes as a function of the correlated yield strength

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