Effects of Surface Treatment on Strength And Hardness of Aluminum Alloy/ Galvanised Steel Resistant Spot Weld-Zn Coated Single Lap Joint

In manufacturing, joining dissimilar metals is a crucial challenge. This study looked into the lap joining of galvanised steel to aluminum sheets (AA5052) using different materials by using a spraying technique to introduce a zinc conductive interlayer. Therefore an experimental investigation into the effects of alkaline treatment was conducted using potassium permanganate (KMnO₄) and hydrogen peroxide (H₂O₂) at different immersion times (0, 10, 20 and 30 minutes). Zinc-rich layer was applied to the treated samples and single lap joints were welded using resistance spot welding (RSW) at 7 kA for 5 seconds. The resulting treated samples underwent comprehensive characterisation using several techniques, including macroscopic observation, surface roughness, nugget size measurement, tensile test, Vicker microhardness, pH measurement, and conductivity test. The results indicated that KMnO₄ exhibited a higher etching rate and greater material removal during the chemical treatment than to H₂O₂ . This resulted in the breakdown of the oxide layer on the metal surface, yielding increased surface roughness and improved conductivity for galvanised steel and AA5052 treated with KMnO₄. The pH of the treated sample rose with prolonged immersion time, with KMnO₄ exhibiting a higher pH value (9.48) compared to H₂O₂ (3.80) at the optimal immersion duration of 30 minutes. This condition resulted in an increased heat input, potentially enlarging the weld nugget diameter and thereby significantly enhancing both weld strength and hardness.