Fig. 10 shows the trend in the hardness evolution (HBW), at different temperatures and times of the precipitation hardening treatment (T6). The maximum hardness value (125 HBW) was obtained with a solution heat treatment at 540 1C for a period of 15 min followed by an artificial aging treatment at 180 1C for 3 h. Similar results were obtained with a solution heat treatmentof 2 h and aging for 4 h at the same temperatures. It might be possible that, with aging heat treatments longer than 8 h, new maximum values of hardness could be obtained. The maximum hardness obtained for this alloy, heat treated with the standard T6 heat treatment, was 75 HB and 70 HB casted in sand and permanent mould, respectively [22].