Aluminum alloys precipitation hardening

A. Denquin, D. Allehaux, M. Campagnac, and G. Lapasset, Microstructure and Mechanical Evolutions within Friction Stir Welds of Precipitation Hardened Aluminum Alloys, Mater. Sci. Forum, Vol 426-432, 2003, p 2921-2926... 

Table 7.44 Galvanic effects in precipitation hardened aluminum alloys.

FIG. 3—The deleterious effect of aqueous chloride solution on the LCF life of a precipitation hardened aluminum alloy [35]. 

The loops around the precipitates act as stress concentrators. They exert shearing stresses in addition to the applied stress on the particles. When enough of them have accumulated, the precipitates will be plastically sheared as the loops disappear one by one. This is the basis of a theory of precipitation hardening in an aluminum-copper alloy by Fisher, Hart, and Pry (1953). The precipitate in this case is CuA12, and the precipitates cause an increment of hardening added to the hardness of the solid-solution (Al-Cu) matrix. Quantitative agreement with experimental measurements is fair. 

Figure 6.5 Two regimes of precipitation hardening in an aluminum-copper alloy.

Age-hardened alloys, 17 102-103 Age hardening, of aluminum alloys, 2 332t Age-hardening precipitates, 13 512 Agency for Toxic Substances and Disease Registry, 16 51... 

AA. Aluminum Association produced a four-digit system for wrought aluminum alloys and a three-digit system for cast alloys. Examples are alloys 6010 (wrought) and 356 (cast). A temper designation is also required. It follows the alloy designation and indicates the heat-treated or mechanically worked condition of the alloy such as 6010-T6. The T6 suffix indicates the alloy is in the precipitation hardened condition for optimum strength. 

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