The feasibility of friction stir welding to joining of AC4CH semisolid cast aluminum alloy plates and the influence of joining condition on the mechanical properties of the joint were investigated. Excessive heat input conditions with high tool rotational speed and low welding speed results in a formation of large burrs. Although the hardness of the stir zone is not affected by the welding condition, the welding speed as low as 1 mm/s forms heat affected zones softer than the stir zone on both sides. Better mechanical properties, such as the tensile strength approximately 82% of the base metal and the elongation exceeding the base metal, is obtained under low heat input conditions.

The 6061-T6 sheet and the DP 780 steel sheet were joined under the condition with the gap length d of 1.17 to 1.42 mm and discharge energy W of 3.0 kJ. The impact speed ranged from 430 to 460 m/s. The weld width showed a tendency to increase due to the increase of the collision speed. However, when the gap length exceeds 1.59 mm (impact speed of >460 m/s), the weld width became narrow. Considering that the electromagnetic force continues to apply on the flyer sheet after collides with the fixed sheet, it is desirable to perform the welding in a time shorter than the time t_m when the collision time reaches the maximum current value. Therefore, the collision time is considered to be one of factors that affect the welding condition. As a result of experiments in consideration of above conditions, it was possible to achieve a strong lap joint of the 6061-T6 sheet and the DP 980 steel sheet, although the welding condition was limited as compared with the case of the DP 780 steel sheet. Thus, sound lap joint between 6061-T6 sheet and high-tensile steel sheet with 1 GPa class was achieved by magnetic pulse welding.

The effect of aluminum acetate coating treatment on the bod strength of the solid-state bonded interface of A6061 aluminum alloy and high-tensile steel plate was investigated by SEM observation of fractured surfaces and interfacial microstructures. The surface of the aluminum alloy was coated by boiling in 5% aqueous solution of NaOH for 20 s and 99.7% acetic acid. Bonding process was performed at bonding temperature of 713–753 K under a load of 20 MPa and bonding time of 900 s. As the result of this study, it was found that the bond strength of the joint increased with the rise in bonding temperature regardless of metal salt coating treatment. Also, it was revealed that with metal salt coating treatment, high tensile strength joint can be obtained lower bonding temperature. From this experimental results, it is inferred that metal salt coating treatment is effective in removing the oxide film and substitution to an aluminum acetate on the aluminum alloy surface.