Bake hardening of nanograin AA7075 aluminum alloy

In the present work, the bake hardening of nanostructured AA7075 aluminum alloy was compared with that of its coarse-grain counterpart. Surface severe plastic deformation (SSPD) was used to produce nanograin layers on both surfaces of workpieces. The nanostructured layers were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The thickness of nanostructured layer, having the grains of 50–110 nm, was about 75 μm on each side of workpiece. The bake hardenability of nanograin and coarse-grain AA7075 was then compared by pre-straining to 2, 4 and 6% followed by baking at 100 °C and 200 °C for 20 min. Comparing to coarse-grain case, there was about 88–100% increase in bake hardenability and about 36–38% increase in yield strength after the bake hardening of present nanograin AA7075. Such an increase in bake hardenability and strength was achieved when the thickness of two nanograin layers was about only one-tenth of the whole thickness.

► The bake hardening behavior of AA7075 was studied and compared with its coarse-grain counterpart.
► Nanograin AA7075 exhibited 88–100% increase in bake hardenability.
► Nanograin AA7075 exhibited 36–38% increase in final yield strength after baking.
► Maximum bake hardenability and final yield stress were about 185 MPa and 719 MPa.