Improvement of Mechanical Properties of Magnesium Alloy ZK60 by Asymmetric Reduction Rolling

doi:10.1007/s40195-017-0649-5

Abstract

Abstract:

The improvement of mechanical properties of ZK60 processed by asymmetric reduction rolling (ARR) was investigated in this paper. The grain refinement and basal texture intensity decrease were attributed to the introduction of shear stress produced by ARR process. Compared to conventional symmetrical rolled (SR) ZK60 alloys, ARRed ZK60 exhibited finer, more homogeneous grains and higher mechanical properties. The intensity of basal texture of ARRed ZK60 after annealing was lower than that of SRed ZK60 after annealing. ZK60 sheet with good combination of strength and ductility could be obtained by ARR process. The yield strength (YS) and ultimate tensile strength (UTS) of the ARRed ZK60 sheet were increased 150% and 91.3%, compared to those of SRed ZK60 sheet, from 80 to 200 MPa and from 140 to 264 MPa, respectively. Simultaneously, the elongation to failure increased by 68.75% in the ARR sheet (27%) when compared to that of the SR sheet (16%).

Key words: ZK60, ARR, Microstructure, Texture, Mechanical properties

Ling Wang, Yi-Quan Zhao, Hong-Mei Chen, Jing Zhang, Yan-Dong Liu, Yi-Nong Wang. Improvement of Mechanical Properties of Magnesium Alloy ZK60 by Asymmetric Reduction Rolling[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(1): 63-70.

Figures/Tables 11

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
Thermal expansion
Heat capacity	N(MM² °C)^-1	1.7675
Interface heat transfer coefficient	N(sMM² °C)^-1	4.5
Thermal expansion		2.2 × 10^-5
Convection coefficient	N(sMM °C)^-1	0.2

Fig. 2 Effective stress distributions of the rolling sheets with different reductions obtained from FE simulation: a 25%, b 50%, c 65% of the ARR sheet; d 25%, e 50%, f 65% of the SR sheet

Fig. 3 Effective strain distributions of the rolling sheets with 25% reductions obtained from FE simulation: a the ARR sheet; b the SR sheet

Fig. 4 Optical micrographs of ZK60 a the as-received ZK60; b the as-homogenized ZK60

Fig. 5 Optical microstructures of ZK60 subjected to repeated SR and annealing at 450 °C: a the first SRed; b the first SRed and annealed; c the second SRed; d the second SRed and annealed

Fig. 6 Optical microstructures of ZK60 subjected to repeated ARR and annealing at 450 °C: a the first ARRed; b the first AARed and annealed; c the second ARRed; d the second ARRed and annealed

Fig. 7 Details of black area in the first-pass ARRed ZK60 sheets

Fig. 8 {0002} pole figure of annealed ZK60 sheets process by the second pass of a SR, b ARR

Fig. 9 Stress-strain relations of ZK60 sheets processed by SR and ARR in annealed condition

Table 2 Comparisons of the room temperature properties of ZK60 alloy using different processings

No.	YTS (MPa)	UTS (MPa)	Elongation (%)	Strain rate (s^-1)	Processing method	References
1	250	350	6	2 × 10^-3	Twin roll cast + rolling at 350 °C	[19]
2	199	306	24	6 × 10^-4	Hot rolling at 400 °C	[20]
3	278	342	18	Not support	Twin roll cast + rolling at 300 °C	[9]
4	200	360	25	5 × 10^-4	12P ECAP at 300 °C	[21]
5	396	440	9	5 × 10^-4	12p ECAP at 300 °C + cold rolling	[21]
6	150	310	30	3.3 × 10^-3	4P ECAP at 250 °C	[22]
7	215	289	37	1 × 10^-3	4P CEC at 230 °C	[23]
8	225	285	25	1 × 10^-3	5P RU at 250 °C	[12]
9	135	285	34	1 × 10^-3	3P RU at 250 °C + sheet extrusion at 220 °C	[12]
10	310	351	17	1 × 10^-3	DE + ECAP, 2p °C at 350 °C	[13]
11	269	315	12	1 × 10^-3	DE at 380 °C	[24]
12	266	175	32	1 × 10^-3	4p ECAP Bc at 240 °C + 4p Bc at 180 °C	[24]
13	80	140	16	1 × 10^-3	SR at 450 °C	Present work
14	200	264	27	1 × 10^-3	ARR at 450 °C	Present work

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