ABSTRACT
The age-hardening alloys add a new variable to hot-working parameters insofar as their structure is not always de‰ned by current temperature, but by thermal history because of their penchant for metastable structures. Their hot-working behavior is worthy of separate discussion from solute or dispersoid alloys of Al because their wide range of microstructural variations with time t and temperature T can lead to a strength dependence on T which may be higher or low than that of pure Al. In addition, the microstructure may undergo change during deformation partly due to time at elevated T and partly due to strain inducement. These can lead to an evolution of substructure and a §ow curve, which are quite different from a single-phase Al alloy. It is wise to clarify beforehand the basic principles of precipitation microstructures, stressing aspects relevant to hot working. For a comprehensive explanation, the book by I. Polmear is recommended. Later, the discussion will extend to the integration of forming and precipitation; additional aspects are presented in thermo-mechanical processing (Chapter 12) and in extrusion (Chapter 14). The effects of particles on creep are described in Section 9.6.
