||The embedded-rod welding tools are used to conduct the friction stir spot welding for the lap of the low carbon steel and aluminum alloy sheets. The theoretical model is used to analyze this lap process and to explore the effects of operating parameters on the plastic flow and temperature distribution for the low carbon steel and aluminum sheets. |
When the Al alloy is placed on the top with the plunge depth of 3 mm, the maximum failure load can achieve 16 kN after 100 s lap welding, and the bonded region in this fractured surface is elliptic. Observing the bonded region in this fractured surface and the theoretical temperature distribution, it is found that the boundary of a bonded region is in consistent with the 460°C isotherm. Thus, the predicted temperature larger than 460°C can form the IMC of aluminum and steel. Theoretical analysis is also found that the bonded area is inversely proportional to the length of the lapped specimens, and proportional to the load and rotating speed.
When the steel is placed on the top and the dwell time of 35 s, the aluminum alloy in the central area near the faying surface has melted. Theoretical simulations can predicted the 652°C isotherm (the liquidus of Al alloy). Theoretical simulations show the smaller the friction coefficient between the tool and the workpiece, the smaller temperature of the faying surface, but the upper plate having a high thermal conductivity (e.g. aluminum or copper) will decrease this temperature, which is clearly greater than the effect of reducing the coefficient of friction. To achieve the temperature of 652°C, we can increase dwell time, increase the coefficient of friction, or reduce the thickness of the lower plate of aluminum, and reduce the thermal conductivity of the upper plate.