Natural Ageing
The process that can alter the hardness and strength in some alloys after a period of time at ambient (room) temperature. It is caused by the spontaneous precipitation of constituents from a super-saturated solid solution. Generally it increases mechanical properties but can also, in some circumstances, cause loss of properties by over-ageing.
Related terms: Age Hardening, Ageing, Over-ageing, Precipitation Hardening
Non-Heat Treatable Alloy
An alloy, from the 1xxx, 3xxx and 5xxx series that are incapable of being strengthened by thermal treatment. These alloys gain their strength from cold-working.