Friction Stir Welding Of Two-piece Magnesium Wheels

In this paper, NZ30 K magnesium alloy plates and 14 inch two-piece NZ30 K wheels with low pressure die casting were subjected to friction stir welding(FSW). The effects of FSW tool with different pin geometries and welding parameters on weld joints microstructure as well as mechanical properties were investigated. Through optimizing the design of FSW tools, exploring the welding parameters and applying heat treatment after welding, the two-piece wheels were succeeded to be welded, with higher welding joint properties than the parent metal of magnesium alloy wheels.The results indicated that the pin geometries of tool played a decisive role on the microstructure and mechanical properties of welding joint, and the conical thread tools did well than cylinder thread tool. The screw in the pin of FSW tool can facilitate the downward effect, and depth and pitch of screw thread had a great influence on the welding.A well-behaved screw thread tool was used to invest the influence of welding parameters on the microstructure as well as mechanical properties of the welding joint. And the results showed that the best welding joint of NZK plant was found at a tool rotation rate of 800 rpm and a traverse speed of 200mm/min. Both excessively high heat input(excessive high rotation rate or low traverse speed) and insufficient heat input(excessive low rotation rate or high traverse speed) would lead to the weld defects.Compared to NZ30 K plants, FSW of two-piece NZ30 K magnesium alloy wheels required higher heat input, and adjustable-pin was adopted to eliminate key hole at the end of the welding. Tensile stretch tests of welding joints showed that mechanical properties of welding joints were better than the parent material, and the X-ray detection of welding joints showed that the wheels were welded without defects, and two-piece NZ30 K magnesium alloy wheels were succeeded to be welded by friction stir welding.