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Abstract: Electric product house of magnesium alloy sheet is usually obtained by warm stamping owing to its poor plasticity and formability at room temperature. The formability of AZ31B magnesium alloy sheet can be improved by repeated unidirectional bending (RUB) process through control of (0002) basal texture. Compared with as-received sheet, the Erichsen value (IE) of the sheet underwent RUB process increases to 5.90 from 3.53 at room temperature. It is also confirmed that cell phone houses could be stamped successfully in crank press with AZ31B magnesium alloy sheets underwent RUB process. It provides an alternative to the electronics industry in the application of magnesium alloys.46896
Key words: magnesium alloy sheet; repeated unidirectional bending; cold stamping; cell phone house
1 Introduction
Magnesium alloys are the lightest metallic structuralmaterials. Compared with steels and aluminum alloys ,they have not only higher specific strength and rigidity,but also excellent mechanical properties. Their products have been widely used in the aerospace, automobile, electronic information, and civilian household appliances. Although the products of magnesium alloys are mainly formed by casting, their products obtained by stamping will have much broader market, because wrought magnesium alloys have higher strength and better ductility[1−3]. As-rolled wrought magnesium alloy sheets show low plastic deformation at room temperature, because they have strong (0002) basal texture and their non-basal slip systems are hard to activate. However, when temperature comes to 423−673 K, the non-basal slip systems are activated, which reduces the flow stress of magnesium alloys and increases the plastic deformation formability[4−8]. Magnesium alloy products have lower strength and poorer surface quality through hot forming, so cold stamping, carried out by improving the formability of magnesium alloy sheets, gets attractive. At present, the methods of improving the stamping formability of magnesium alloy sheets at room temperature are mainly through the control of (0002) basal texture of magnesium alloy sheets[9]. Majority of the experimental surveys showed that, the basal texture of magnesium alloy sheet could be weakened by cross-rolling and different speed rolling (DSR) process, which enhanced plasticity and stamping formability of magnesium alloy sheets[10−16]. IWANAGA et al[10] also reported that Erichsen value increased significantly at room temperature by weakening (0002) basal plane texture.
Previous researches showed that the repeated unidirectional bending (RUB) process improved cold stamping formability of magnesium alloy sheets by weakening basal texture of sheets[17−18]. However, the research on cold stamping of cell phone house has not been performed for magnesium alloy sheets, and relevant reports have not been seen in other references. Hence, it is very important to investigate the cold deformation behaviors of cell phone house in order to lay a theoretical foundation for cold stamping of magnesium alloys and propel magnesium alloys used in the electronics industry. In this work, experiments and finite element (FE) analysis are performed to investigate the effect of RUB process on cold stamping of magnesium alloy sheets.
2 Experimental
2.1 Preparation of material
The as-received AZ31B sheets, with a thickness of 0.6 mm, were processed by RUB process along the rolled direction (RD). The diagrammatic sketch of RUB is shown in Fig.1, where the magnesium alloy sheet was bent on a cylindrical support under a constant force T with a constant speed v. The bend direction was parallel to the RD direction of the sheet. The radius of the cylindrical support was 1 mm and the bending angle was90˚. In the experiments, six-pass bending was used. The sheets underwent RUB process were annealed at 533 K for 60 min.
Fig.1 Diagrammatic sketch of RUB
2.2 FE simulation of shallow drawing