Assessment of different techniques for quantification of α-Al(FeMn)Si and β-AlFeSi intermetallics in AA 6xxx alloys

Influence of Heat Treatment on the Surface Structure of 6082 Al Alloys

“…However, during heat treatment the b-peaks decrease continuously by increasing holding time, while the a peaks have a more random appearance. This is in contrast to what was observed in bulk material, [2] where the a-peaks grew as the b peaks disappeared. As has been discussed above, it is likely that in the surface zone there is no gradual b to a phase transition, but rather melting of the eutectic and b-phase followed by precipitation of a during subsequent cooling.…”

“…This could be a problem, as for lower temperatures the bulk will not transform in reasonable time, e.g., at 813 K (540°C), it has been reported that nearly no transformation occurred after 20 minutes. [2] The concentration in the surface zone is a result of segregation during solidification toward the surface and thus very high concentrations are obtained. Making a simple Scheil plot of the segregation, Figure 9 gives an approximation of the level of surface segregation that can be expected.…”

“…[18] In many cases, it is important to know when the b to a-phase transformation is completed, and different techniques have been tested to evaluate this. [2] XRD is one possible technique, and with a penetration depth in Al of about 80 lm it is suitable for studies of the segregated surface zone, done in the present research. According to the present XRD measurements, Figures 7 and 8, both intermetallic phases, b and a, are found at the segregation zone of the as-cast billets.…”

“…[1][2][3][4] The b-AlFeSi phase is an undesirable phase due to formation of hot cracking and surface defects during subsequent procedures, e.g., extrusion. [5,6] To obtain high surface-quality extruded products, at reasonable extrusion rates, the as-cast billets need to be homogenized before extrusion.…”

“…[5,6] To obtain high surface-quality extruded products, at reasonable extrusion rates, the as-cast billets need to be homogenized before extrusion. [1,2,6] The homogenization temperature, holding time, and cooling rate influence the heat-treated microstructure. [6] Increasing the heat treatment temperature increases both the solubility and the diffusion coefficient, [7] and it is known that the percentage of a-phase will be increased by time during homogenization.…”