Plain heat treatment hardening (English name ?) use the ability of a certain metals to change their own metal structure to different forms. These changes are nearly always the results of temperature. As such there is no need for any alloy elements and as such it is a different hardening method to precipitation hardening. A good example of this plain hear hardening is normal iron/steel. Heat it and then cool it very rapidly and it will became very hard (and brittle). This can then be soften again by mildly heating it for a given period of time at a lower temperature. Allowing portions of the dissimilarity to morph back to less hard grid structures. Wouter
Do you mean "case" hardening? Which typically happens with tool steels and/or annealing where a metal is "softened" for machining or bending and then hardened again afterwards. There are a heap of different techniques for different desired results. Don't underestimate the effects of age hardening on Aluminum though. In some climates it can be very surprising!
