Effect of heat input on corrosion behavior of automotive zinc-coated steel joint

Abstract

Abstract Lately, coated steel sheets have replaced bare steel in the automotive sectors due to their corrosion protection. Among them, zinc-coated high strength interstitial free (HIF) steel is widely used due to its durability, formability, good surface finish, impact resistance, and corrosion resistance. However, joining galvannealed (GA) steel using conventional fusion welding processes is challenging as it results in porosity and potentially harmful fumes. To overcome these challenges, this work uses a pulse MIG (metal inert gas) brazing technique to join the HIF-GA steel sheet with a lap joint configuration utilizing Cu-Si base filler wire (CuSi3Mn1) in an argon atmosphere. The study aims to evaluate the effect of heat input on bead geometry and Zn degradation in MIG brazed joints by adjusting the current from 40 to 60 A and brazing speed from 400 to 500 mm min−1. It is observed that the heat input is inversely proportional to the wetting angle and directly proportional to the bead width, leg length, and cross-sectional area. Heat input influences Zn degradation on both the front (at the toe) and back sides of the lap joint. The corrosion behavior of joints is studied using an electrochemical test (in 3.5% NaCl solution) and a salt spray test (in 5% NaCl solution). Further, the Zn degradation is analyzed with EDS line scanning to understand the corrosion resistance of the MIG brazed joints. A potentiostatic polarization study is also conducted to determine the corrosion rate using a Tafel plot. It is found that the lowest corrosion rate in base metal (BM) increased from 0.88 to 12.26 mm year−1 with the increase in heat input from 61 to 113 J mm−1.