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

摘要

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 mu m 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 mu m 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 mu m below the surface.