No abstract

No abstract

In high strength 6000 series alloys dispersoids that form during heating to the homogenization temperature are used to improve fracture toughness and suppress grain growth during the extrusion process. However, these dispersoids can act as heterogeneous nucleation sites for nonhardening Mg-Si precipitates if quenching after extrusion is delayed. This leads to a reduced level of Mg and Si in solid solution and hence lower achievable strength and hardness. This phenomenon is called quench sensitivity. In this study, the hardening response of several 6000 series aluminium alloys is related to microstructural features, especially dispersoid density. Therefore, the alloys were quenched at varying rates after extrusion and age hardened to peak strength. Quench sensitivity is related to dispersoid density as well as to the enthalpy related to the precipitation of Mg-Si phase measured by DSC. The results suggest that in alloys containing dispersoids, quench sensitivity is primarily determined by the number density of dispersoids. However, effects associated with elements in solid solution cannot be ruled out. TEM investigations suggest that not only the general reduction of Mg and Si is responsible for the reduced mechanical properties, but that an inhomogeneous distribution of hardening precipitates might be another determining factor.

The effect of iron content, ranging from 0.1 to 0.5 wt pct, on the formation of Fe-containing intermetallic phases in a cast 6060 aluminum alloy was investigated. Various characterization techniques, including optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to examine the identity, morphology, and prevalence of the Fe-Al and Fe-Al-Si intermetallic phases. The predominant phase is found to be b-Al 5 FeSi at lower Fe levels, but this is replaced by a-AlFeSi (bcc structure) with increasing Fe content. The Fe containing intermetallic phases observed are compared to those predicted using the Scheil module of THERMO-CALC software, and the similarities and discrepancies are discussed.

No abstract