Impulsive High Current Density Spot Welding of Aluminum Alloy to Mild Steel (Report 2)

Effect of Current Direction on Weldability

Abstract

Effect of welding current direction on tensile shear strength (TSS) of joints has been studiedin the weld of aluminum alloy (0.8t 5052) to mild steel (0.8t SPCC). In this welding, uni-directional discharge current from capacitors is utilized as welding current. Therefore the polar effect, the difference of weldability caused by current direction relative to the position of dissimilar metals to be joined, has been investigated. It was found that higher TSS value was obtained using welding current with direction from SPCC to 5052 (refered this as SPCC (+) and the contrary as 5052 (+)). The difference of TSS was about 20 kg/spot with R-type electrode tips. It became more significant in the case of CF-type electrode tips; obtained TSS of the joint, by the use of welding current with peak value 45.6 kA and peak time 2.8 ms, was about 350 kg/spot under SPCC (+) and 150 kg/spot under 5052 (+) respectively. The shorter the duration of impulsive weld current, this tendency appeared more clearly. Measurement of the voltage between SPCC and 5052 revealed that the polar effect appeared in this faying interface at early stage of the welding process and vanished with metallic contact growth. It is concluded from the results that the polar effect is attributed to the semiconductor property of the surface film of the metal such as oxide film rather than the thermoelectric phenomena of the metals themselves.