When the aluminum was extruded into the through hole and it formed a joint between the upper and lower plates, the ultimatetensile load increased by more than three times that of the samples that did not join in the through hole from 230 kgf to 739 kgf. These results indicate that the addition of this solid “rivet” like section ofthe weld significantly impacts the overall strength of the joint. So,to achieve maximum strength with the process, it is critical that the top and bottom sheet join to one another in the through hole.This “riveted” structure provides additional clinching or normal force that helps hold the weld together similar to how a bolt holds sheets of metal together. This is likely due to expansion of the aluminum from heat during the process and its subsequent cooling and contraction