Most applications of VPDC casting aluminum alloys for the automotive industry are in the area of structural parts, such as chassis and its auxiliaries . Bearing in mind that body structural applications are highly demanding in terms of strength and ductility, the joints that configure these parts must guarantee an adequate mechanical behavior. Furthermore, the process must also show a reduced cycle time and automation potential to fulfill the high manufacturer rate by the automotive industry. Thus, the joining process of these VPDC alloys must be carefully chosen and optimized. Self-piercing rivets have been driving material requirements for many applications, such as auto bodies in the past, pushing the use of high elongation materials to obtain crack-free rivets . The limited weldability of VPDC castings in comparison with other high mechanical properties casting processes, such as low pressure or die gravity casting process, is mainly associated with the higher porosity tendency observed in VPDC when high temperatures are applied, as it occurs during heat treatment and/or welding processes. The porosity formation is associated to the higher gas entrainment and/or die release decomposition typical of HPDC processes.
The high Fe content in the AlMg4Fe2 alloy (1.6 wt. %) ensures reduced die sticking tendency and improved die-casting mold life . This high Mg content alloy (3.95 wt. %) is a natural-hard alloy and exhibits excellent long-term stability in the as-cast state, even at high application temperatures and it presents similar good weldability than 5xxx wrought series .
Figure 9 shows the area of FSW defects in AlSi10MnMg and AlMg4Fe2 welds as a function of welding speed. The area of these defects was calculated from optical micrographs by using the software ImageJ. It is observed that for the same welding speed the area of FSW defects is higher for AlMg4Fe2 than for AlSi10MnMg, except for the highest welding speed when the area of defects is quite similar. This fact highlights the superior friction stir weldability of AlSi10MnMg compared to AlMg4Fe2. 2b1af7f3a8