Nugget growth characteristic for AZ31B magnesium alloy during resistance spot welding

An axisymmetrical finite element model for studying the distribution of temperature for resistance spot welding (RSW) to predict weld nugget growth of AZ31B Mg alloy was developed by employing a contact resistance model based on the microcontact theory. The RSW of a Mg alloy, with regard to nugget formation, consists of the initiation of a nugget in the first cycle, a rapid growth of the nugget in the following 2–3 cycles and a plateau of nugget growth after ∼4 cycles. Because of its high thermal conductivity, low melting point and low volumetric heat capacity, Mg alloy has many characteristics during nugget formation, compared with Al alloy and mild steel. In the RSW of a Mg alloy, the contact resistance in the interface has an important effect on the nugget formation; the welding time is similar to that in Al alloy but smaller than that in low carbon steel; and the welding current lever is required slightly lower than that in Al alloy but higher than that in low carbon steel. The computational simulations based on this model agree well with the experimental data.