Control of hardness distribution in friction stir welded AA2024-T3 aluminum alloy

Abstract

AA 2024-T3 Aluminum alloy plates of 3 mm thickness were friction stir butt welded at a constant rotation speed of 1250 min -1 and welding speeds of 50 and 100 mm/min. Three types of backing materials such as SUS304, pure copper block, and a combination of copper-block with 0.5 mm SUS304 were used. Controls of temperature history were achieved and their effects on microstructures, hardness distributions, and tensile properties of the joints were investigated. Grain size of the stir zone decreased from 7.4 μm in the case of stainless steel to 4.4 and 1.7 μm for the cases of a combination backing type and copper-block respectively. As a result of higher heating/or cooling rates, both higher welding speed and copper-block backing material resulted in increased hardness in HAZ and a maximum value was achieved for the combined backing plate at 100 mm/min of welding speed. Higher peak temperature was beneficial for higher hardness in stir zone while lower one in HAZ. A maximum tensile strength of the joint was achieved at a welding speed of 100 mm/min when the combined backing type was used. The joint efficiency of this case was 93.6% ana this value was tne highest among me present joints. © 2006 The Japan Institute of Metals.