The
Aluminium 6061 T6 heat treatment represents a condition, when the microstructure of aluminium is solutionized, quenched and again heat treated (artificially aged).
Solutionizing is the process of heating the metal to relatively high temperatures (above 500 °C) to allow the dissolution of intermetallic phases into the aluminium metal matrix. Since it is a diffusion controlled process, it depends strongly on temperature and time. The annealed state refers to the soft O temper.
To allow for a good response to the artificial aging step, it is necessary to freeze in the solutionized microstructure, by quenching (rapid cooling).
Because the solubility of Mg and Si in aluminium is low at room temperature, Mg2Si particles will form homogeneously throughout the metal matrix increasing the overall strength. This is called aging.
If aging happens slowly, uncontrolled at room temperature it will be called T4 condition (natural aging).
Aging can also happen at elevated temperatures (150–200°C) for several hours, which allows a better distribution of Mg2Si particles and therefore better strengthening. This artificial aging process refers to T6.
Here is a link to compare the strength increases from 120 MPa (O-Temper) to over 300 MPa (T6) UTS.
Typical applications for
Aluminium 6061 T6 are extrusion products.
To restore the strength of a welded Aluminium 6061 material, a tempering step is necessary, because the metal will be close to O temper near the weld.