Microstructure and properties characteristic during interrupted multi-step aging in Al-Cu-Mg-Ag-Zr alloy

The effects of interrupted multi-step aging on the microstructure and properties of Al-Cu-Mg-Ag-Zr alloy were studied by tensile, hardness, electrical conductivity tests and transmission electron microscopy (TEM). Interrupted multi-step aging delayed the peak aging time compared to one-step aging and kept the same levels of hardness, electrical conductivity, ultimate tensile strength (UTS), yield strength (YS) and elongation as those of the T6 temper alloy while increased the fracture toughness notably. Ω phase and a little θ′ phase precipitated and grew simultaneously in the process of one-step aging at 160°C. During the second-step aging at 65°C of interrupted multi-step aging, no TEM characteristic of Ω precipitates could be found. During the third step of interrupted multi-step aging, Ω began to dominate the microstructure like what happened in the process of one-step aging. The difference of properties between the T6 temper and the interrupted multi-step aged alloys might be related to the different precipitation sequences in the process of the two heat treatment technologies.