The Influence of Paint Bake Cycles on the Mechanical Properties of Spot Friction Joined Aluminium Alloys

The effects of paint bake cycles on the static performance of aluminium alloys joined by the Spot Friction Joining (SFJ) process have been evaluated. The aluminium alloys used for this investigation comprised of either NG5754 or AA6111-T4. Single SFJ welded lap joints were manufactured for each alloy using a common SFJ tool type and parameters optimised to the individual alloy stacks. Samples were then subjected to mechanical testing, or exposed to a typical paint bake cycle of 180°c for 30 minutes prior to mechanical testing. The failure modes obtained from the testing were also examined. The experimental observations suggest that the SFJ joints in the NG5754 alloy becomes brittle as a result of the paint bake cycle and consequently the strength in both lap shear and peel is reduced. The joints in AA6111 demonstrated a slight increase in strength, in line with the expected increase in AA6111 base material strength that would result from such a bake cycle. This information corroborates with published findings for the self pierce riveting process.