Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91

doi:10.1007/s40195-017-0695-z

Acta Metallurgica Sinica (English Letters) ›› 2018, Vol. 31 ›› Issue (7): 673-680.DOI: 10.1007/s40195-017-0695-z

所属专题： 2017-2018镁合金专辑； 2018镁合金专辑

收稿日期:2017-07-17 修回日期:2017-09-18 出版日期:2018-07-10 发布日期:2018-06-06

Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91

Yi-Quan Zhao¹, Hong-Mei Chen², Jing Zhang³, Ru Ma¹, Yan-Dong Liu⁴, Yi-Nong Wang¹, Ling Wang⁵(), Qun Zhang⁶, Wei-Gang Li⁶

1 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
2 Provincial Key Lab of Advanced Welding Technology,Jiangsu University of Science and Technology,Zhenjiang 212003, China
3 School of Metallurgy and Materials Engineering, Jiangsu University of Science and Technology,Zhangjiagang 215600, China
4 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
5 Yingkou Institute of Technology, Yingkou 115014, China
6 Bayuquan Entry-Exit Inspection and Quarantine Bureau,Yingkou 115000, China

Received:2017-07-17 Revised:2017-09-18 Online:2018-07-10 Published:2018-06-06

摘要/Abstract

Abstract:

The influence of asymmetric reduction rolling (ARR) on the microstructure, texture and mechanical properties of AZ91 was investigated. The microstructural characteristics of the AZ91 sheet processed by symmetric rolling (SR) were the twins, intersection of twins and dynamic recrystalization (DRX) grains around the coarse grains and within the twins. However, the amount of twins and DRX grains in ARRed AZ91 was much smaller than that in SRed AZ91. The SRed AZ91 after annealing exhibited fine DRX grains and some coarse grains with a size of ~ 100 μm. The grains in ARRed AZ91 after annealing were much finer and more homogeneous than those in SRed AZ91 after annealing. The intensity of basal texture of ARRed AZ91 after annealing was lower than that of SRed AZ91 rolling after annealing. The average Schmid factor of ARRed AZ91 is 0.34, which is higher than that of SRed AZ91. The yield strength and ultimate tensile strength of the ARRed AZ91 sheet were increased to 16.1% and 31.8% compared to SRed AZ91 sheet, from 155 to 180 MPa, and from 220 to 290 MPa, respectively. The improvement of mechanical properties in ARRed AZ91 after annealing was attributed to much finer, more homogeneous DRX grains and weaker basal texture.

Key words: AZ91, Asymmetric reduction rolling, Microstructure, Texture, Mechanical properties

. [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(7): 673-680.

Yi-Quan Zhao, Hong-Mei Chen, Jing Zhang, Ru Ma, Yan-Dong Liu, Yi-Nong Wang, Ling Wang, Qun Zhang, Wei-Gang Li. Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(7): 673-680.

图/表 12

Fig. 1 Schematic of the ARR process a initial stage; b stable rolling stage

Table 1 Parameters of ARR FE simulation

Parameters	Unit	Value
Friction coefficient
Roll-sheet, μ₁		0.3
Support plate-sheet, μ₂		0.1
Thermal properties
Thermal conductivity	N(s °C)^-1	159
Heat capacity	N(MM²°C)^-1	1.7675
Interface heat transfer coefficient	N(s MM²°C)^-1	4.5
Thermal expansion
Thermal expansion		2.2 × 10^-5
Convection coefficient	N(s MM °C)^-1	0.2

Fig. 2 Effective stress and strain distributions of AZ91 sheets with a 30% reduction obtained from FE simulation: a effective stress distribution of ARR; b effective stress distribution of SR; c effective strain distribution of ARR; d effective strain distribution of SR

Fig. 3 Schematic illustration of the sample for rolling taken from a cast ingot

Fig. 4 Optical micrographs of the as-homogenized AZ91

Fig. 5 Optical microstructure of a as SRed AZ91; b SRed AZ91 in annealed condition

Fig. 6 Optical microstructure of a, b as ARRed AZ91 sheet; c ARRed AZ91 in annealed condition

Fig. 7 Details of black area in ARRed AZ91 rolling sheets: a SEM image; b EDS result for phase A; c EDS result for phase B

Fig. 8 Inverse pole figure (IPF) maps of the rolled AZ91 Mg alloy obtained by EBSD: a SRed AZ91; b ARRed AZ91 Figure 9 shows Schmid factor (SF) distribution maps for basal <a> slip system of AZ91 sheets processed by ARR and SR process, obtained by EBSD analysis. It can be observed that for SR sheet with a stronger basal texture, the average of Schmid factor (ASF) in the basal plane is 0.29, while for ARR sheet with a weakened basal texture that is 0.34, which is slightly higher than that of SR sheet. Thus, it is more easy to activate the basal slip during deformation, which results in an improvement in the plasticity of AZ91 alloys.

Fig. 9 Schmid factor of AZ91 sheets processed by a ARR; b SR with a 30% reduction

Fig. 10 Stress-strain relations of AZ91 processed by SR and ARR

Table 2 Comparisons of the room temperature properties of AZ91 alloy using different processing

Processing method	YTS (MPa)	UTS (MPa)	Elongation (%)	Reference
T4 treated AZ91	150	210	10	[27]
SRed AZ91	155	220	10	Present work
ARRed AZ91	180	290	15	Present work
As rolled AZ91	175	260	6	[28]
MDF AZ91-350-1P	135	220	3	[29]
MDF AZ91-400-1P	150	250	3.5	[29]

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Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91

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