Fluidized Bed Heat Treatment of Cast Al-Si-Cu-Mg Alloys

The effects of fluidized bed heat treatment on the microstructural and mechanical properties of Al-Si-Cu-Mg cast alloys, namely,3 54 and 319, were studied. The heating rate in fluidized beds (FBs) is greater vis-a`-vis conventional electrical resistancef urnaces (CFs). The high heating ratei nF Bs increases the kinetics of metallurgical phenomena such as Si fragmentation and spherodization during solution heat treatment, as well as the precipitation rate of phases such as Al 5 Cu 2 Mg 8 Si 6 and Al 2 Cu during aging. It is observed that the dissolution rate of phases such as Mg 2 Si and Al 5 Cu 2 Mg 8 Si 6 takes place very rapidly.The solution heat treatment of 319 alloy using FB results in complete dissolution of Mg 2 Si and Al 5 Cu 2 Mg 8 Si 6 particleswithin 45 minutes. However,for phasessuch as Al 2 Cu and Fe-rich intermetallics, the dissolution rate is relatively slow. Even on prolonged solution heat treatment for 6hours, these phases do not dissolvecompletely.Itisobserved that incompletedissolution of the Al 2 Cu phase does not significantly affect tensile properties of T4-treated alloys. The optimum solution heat-treatment time in FB for both 354 and 319 alloys is 45 minutes at 527 ° Ca nd 493 ° C, respectively.Thermal analysis shows an exothermic peak owing to recrystallization and coarsening of eutectic grains during solution heat treatment. The high heating rate in FB causesthis transformation to take placea talower temperature than in CF.I ti so bserved that the nucleation rate of Al 5 Cu 2 Mg 8 Si 6 during agingi nF Bi sg reater than using CF.T hermal analysis of samplesd uring the ramp-upstage while agingusing FB did not showany phase transformation, while those using CF showt wo endothermic transformations, which are most likely due to the dissolution of GP zones or the co-cluster of solutes. Aging at 200 ° Cresults in agreater number density of precipitatesthan those at 240 ° C. Thet ensile strength of samplesa ged at 200 ° Ci sg reater than those aged at 240 ° C, because the amount of precipitates formed at 200 ° Ci sg reater than that at 240 ° C. The total heat-treatment time for T6 temper is less than 2h ours in FBs, which is as ignificant reduction in heat-treatment time, as well as energy consumption.