Linked from
The 15 pages that link to Work hardening, each with the reason it gives.
AlloyRelated: Deforming an alloy can raise its strength by increasing dislocation density.
BronzeRelated: Hammering bronze can strengthen it, though excessive deformation can make it crack.
Aluminum canRelated: Forming and ironing change the mechanical properties of can-wall aluminum.
Aluminium foilRelated: Rolling hardens foil, so manufacturers may anneal it to restore flexibility.