Article history: Received 11 April 2010 Received in revised form 7 November 2010 Accepted 28 November 2010 Available online 7 December 2010

Keywords: Magnesium alloy sheet RUB Texture Stamping formability Cell phone housing 46896

The repeated unidirectional bending (RUB) process was carried out on an AZ31B magnesium alloy in order to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of the RUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach 1.5 at room temperature. It was also confirmed that cell phone housings can be stamped successfully in crank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stamping formability at room temperature can be attributed to the texture modifications, which led to a lower yield strength, a larger fracture elongation, a smaller Lankford value (r-value) and a larger strain hardening

exponent (n-value).

© 2010 Elsevier B.V. All rights reserved 

1. Introduction

Nowadays, the products of magnesium alloys, mainly formed bycastinganddie-casting,areusedintheaerospace,automobile,civilian household appliances. Compared with casting and die-casting, plastic forming technology seems to be more attractive because of its competitive productivity and performance. Among the fabrication processes of plastic forming, stamping of magnesium alloy sheets is especially important for the production of thin-walled structural components (Chen and Huang, 2003). However, magnesium alloy sheets have low ductility at room temperature due to its strong (0 0 0 2) basal texture, as shown in the literature (Doege and Droder, 2001). Mori and Tsuji (2007) investigated cold deep drawing of commercial magnesium alloy sheets, they demonstrated that the limiting drawing ratio of rolled AZ31 magnesium alloy sheets annealed at 773 K can reach 1.7. Mori et al. (2009) have shown that a two-stage cold stamping process are also helpful for forming magnesium alloy cups. Watanabe et al. (2004) suggested the ductility of magnesium alloy sheets can be improved by reducing (0 0 0 2) basal texture at room temperature. The limiting drawing ratio for the cold deep drawing of commercial magnesium alloy sheets can be improved from 1.2 to 1.4 by reducing (0 0 0 2) basal plane texture (Iwanaga et al., 2004). It is well-known that equal channel angular pressing (ECAP) is an effective method to obtain a tilted basal texture, which improved significantly the tensile elongation (Kim et al., 2003). But it is hard for ECAP to fabricate thin sheet. Recently, it is reported that a rolled magnesium alloy sheet, with a tiled texture obtained by cross-roll rolling (Chino et al., 2006) and different speed rolling (DSR) process (X.S. Huang et al., 2009), exhibit higher stamping formability compared with a rolled magnesium alloy sheet by normal-roll rolling. It is therefore important to improve the formability at room temperature for a wide use of magnesium alloy sheets by changing or weakening the basal texture. Older versions of the ASM Metals Handbook (1969) on forming refer to a “special bending sheet,” which was produced by Dow Magnesium. The special bending sheet with a modified crystallographic texture, had better forming characteristics than conventional AZ31 sheet. Previous study (G.S. Huang et al., 2009) revealed that the RUB process also improved the stretch forming of magnesium alloy sheets by weakening basal texture of sheets. The Erichsen values of the RUB processed sheet significantly increased from 3.53 to 5.90 in comparison with the cold-rolled magnesium alloy sheet. However, up to now, few researchers made efforts to study the cold stamping formability of the magnesium alloy sheets. Cold stamping products, such as housings of laptop computers and cell phones, have not been reported in other investigations. Hence, it is important to investigate the cold deformation behaviors so as to establish fundamental knowledge of the cold forming technology of magnesium alloy In this paper, an investigation of the drawability of RUB processed AZ31 magnesium alloy sheet was performed at room temperature using uniaxial tensile tests, deep drawing and cold stamping of a cell phone housing. The performance of RUB sheet was compared with that of the as-received sheet.