Ultrasonic Evaluation at the Interface of Aluminum/Steel Obtained by TIG Welding

Abstract

Aluminum filler (Al-5%Si) is bonded on steel substrate by gas tungsten arc welding process under different current setting conditions. After welding a thorough metallographic analyses using optical and scanning electron microscopy were carried out to observe Al-Steel interface. Ultrasonic measurements by immersion and scanning acoustic microscopy were made to characterise the bond at Al-Steel interface. The ultrasonic wave reflected from the Al-Steel interface clearly indicated the more debonded area when the welding current is changed from direct current straight polarity (DCSP) mode to alternate current high frequency (ACHF) or the welding current in case of current for DCSP mode is reduced. This may be attributed either adequate amount of oxides along with intermediate phase make the bond interface rough and uneven due to introduction of ACHF mode or debonded areas are higher due to lower heat input when the current reduced to 125 amps from 150 amps in DCSP mode. Whereas smooth and even bond interface due to uniform heat input resulted stable Al-Steel interface and the mapping of bonded area by ultrasonic measurement showed spectrum of minimum peak for using current of 150 amps in DC mode. Thus the non-destructive assessments of interface between dissimilar materials through ultrasonic measurements could be important tools for evaluating the state of the bond.