Impact of Aluminum in Comparison to Silicon on Liquid Metal Embrittlement of 3rd Generation AHSS

The impact of Si on Zn-induced liquid metal embrittlement (LME) in 3 rd generation advanced high strength steels (AHSS) during resistance spot welding has been widely studied, but the effect of Al is rather unknown. This study investigates the substitution of Al for Si by analyzing two steels with the fixed C and Mn-contents of 0.2 and 3 wt.-% respectively. Si and Al-contents are both set to 1.4 wt.-%. To minimize microstructural effects, all steels were quenched and tempered before electro-galvanizing. The effects of Si and Al were examined using hot tensile testing (600 – 900 °C, in 50 K steps) on a Gleeble 3800, resistance spot welding with prolonged welding times, thermodynamic calculations with Thermo-calc® and dilatometry. Results indicate that the use of either Si or Al increases the LME-susceptibility but substituting Al for Si significantly reduces Zn-induced LME-cracking. In hot tensile testing, higher testing temperatures generally increase the steel’s vulnerability to LME. But comparing both alloying elements to one another, Si causes a higher LME-susceptibility.