Achieving thin wall and high surface quality of magnesium alloy tubes in combined process of hollow sinking after die-less mandrel drawing

Abstract

Dimensions and surface roughness of magnesium alloy tubes were evaluated to elucidate the flattening behavior of asperity on the outer surface and the optimal condition for achieving thin wall and high surface quality in the combined process of the hollow sinking after die-less mandrel drawing. ZM21 tubes were drawn using a die after die-less mandrel drawing. Dimensions and surface roughness were measured, and the stress state of the asperity during hollow sinking was evaluated using finite element and slab methods. The results indicated that in hollow sinking after die-less mandrel drawing when the speed ratio was large, both a thin wall and high inner and outer surface qualities can be achieved under low die reduction, where the outer surface roughness was the least, owing to relatively large die pressure and drawing stress. Additionally, enhancing the flattening of the asperity due to bulk plastic deformation in tension was difficult even if drawing stress increased when the speed ratio in die-less mandrel drawing was large. Therefore, when the speed ratio of the die-less mandrel drawing was large before hollow sinking, the largest outer surface flattening was achieved under low die reduction, wherein die pressure was large.