Welding-time-temperature-precipitation-diagram of aluminium alloy 6082 T6Wednesday (08.11.2017) 12:00 - 12:20 Part of:
Aluminium-magnesium-silicon wrought alloys are widely used for industrial applications. This is due to their excellent relationship of strength to density, high corrosion resistance and good weldability. The high strength of 6XXX-aluminium alloys is mainly obtained by precipitation hardening. Welding is one of the most important joining processes and is often used for aluminium alloys. During welding, different maximum temperatures are achieved in the heat affected zone, depending on different factors, like weld seam geometry, welding parameters and distance to the weld seam. Since the strength-increasing precipitates are dissolved at higher temperatures, the welding of precipitation-hardened aluminium alloys leads to a localized softening in the heat affected zone, i.e. inhomogeneous material properties. To understand these processes, knowledge about the occurring dissolution and precipitation reactions during the welding process is crucial.
Welding is characterized by high heating rates, high peak temperatures and almost no soaking at maximum temperature. This thermal load during welding is very different from conventional heat treatment. For this reason, conventional time-temperature-transformation (TTT) diagrams cannot be used for welding. In order to estimate the microstructures after welding, welding-TTT-diagrams are well known for steels. For aluminium alloys such diagrams are not yet available.
The precipitation behaviour of alloy EN AW 6082 T6 was investigated in dependence of maximum temperature, soaking time and cooling rate. Differential scanning calorimetry was used to record in-situ the precipitation behaviour during the cooling step. The maximum temperature was varied in the range between 540 and 585 °C. The solution annealing was reduced from the conventional 20 min down to 1 min and cooling rates were examined from 0.01 up to 5 Ks-1. The welding-time-temperature-precipitation (WTTP)-diagram is established.