Alloy Design for Heat Treatment of High Pressure Diecastings

Abstract

Recently, heat treatment technologies have been developed by the CSIRO Light Metals Flagship in Australia that allow the yield stress in conventional aluminium HPDC’s to be more than doubled without encountering problems with blistering or dimensional instability. These procedures involve a severely truncated solution treatment step conducted at lower than normal temperatures followed by quenching and artificial ageing. Typically, heat treated HPDC’s may display increases to the yield stress of around 80 to 100%, but a range of other properties may also be improved such as fatigue resistance, thermal conductivity and fracture resistance for some tempers. However, the HPDC alloys currently used worldwide have not been developed specifically for heat treatment or the optimization of specific properties. In particular, recent work in Al-Si-Cu HPDC alloys has identified ranges of alloys specifically for achieving yield strengths exceeding 400 MPa, or for high strength combined with elevated ductility levels. The role of alloying elements, composition limits and effects on microstructure development are discussed.

The heat treatment of Al–Si–Cu–Mg casting alloys

“…A T5 heat treatment, consisting of a fast cooling after solidification together with an artificial ageing is instead used to improve the strength. A short solution treatment prior to artificial ageing has however been shown to be successful in increasing the yield strength above that of a T5 heat treatment without occurrence of blisters [22]. 2.…”

Progress on the heat treatment of high pressure die castings

“…The times to reach peak hardness for each solution treatment temperature were similar, although the actual peak hardness values and tensile properties decreased as the solution treatment temperature was reduced ( Fig. 10.5) (Lumley et al, 2007b). Figure 10.5 also shows the influence of melt velocity (at the gate) on the tensile properties in the T6 treated HPDCs.…”

“…However, it has been shown recently that significant responses to age hardening are still possible if solution treatment temperatures and times are reduced (e.g. Lumley et al, 2005Lumley et al, , 2006Lumley et al, , 2007aLumley et al, , 2007b. As a result, the mechanical properties of the common HPDC alloys can be substantially improved.…”

“…Lumley et al, , 2008aLumley et al, , 2009 Comparisons of the surfaces and internal microstructures of an A360 alloy solution treated under different conditions (Lumley et al, 2007b).…”

“…Further investigations on the effect of solution treatment temperature were conducted on a different alloy having the composition Al-8.8Si-0.86Fe-3Cu-0.2Mn-0.22Mg-0.59Zn-(<0.2 other) which corresponded to alloy C380 in Table 10.1 (Lumley et al, 2007a). In this case, substantial responses to age hardening were achieved over the range of 440°C up to 490°C, with solution treatment of 15 minutes immersion, followed by water quenching and ageing at 150°C.…”