Surface modifications of a cold rolled 2024 Al alloy by high current pulsed electron beams

Overview & Synopsis

This work investigates the effect of a high current pulsed electron beam (HCPEB) surface treatment on a precipitation hardened and cold rolled (T9treated: 155 HV in hardness) 2024 Al alloy and details the modifications encountered in the different surface and sub-surface layers. The rapidly solidified top surface melted layer (less than 10 μm in thickness) was a Cu-enriched Al supersaturated solid solution that generated improved corrosion properties. The absence of second phase precipitate resulted in a drastic softening of this melted layer (108 HV). Below the melted layer, the sub-surface heat affected zone that remained solid was also softened (down to 145 HV) due essentially to the solid state dissolution of the S-precipitates, recrystallization and annealing of dislocations. The heat affected zone could extend down to100 μm below the surface after 24 pulses of irradiation. Finally, the stress affected zone was characterized by an additional hardening (8% increase, up to 168 HV) generated by the thermo-mechanical stresses induced by the pulsed electron beam. This “deep-hardening” in the stress affected zone extended for all samples down to about 400 μm below the surface.