EFFECT OF ALLOYING ELEMENTS AND DENDRITE ARM SPACING ON THE MICROSTRUCTURE AND HARDNESS OF AN AL-SI-CU-MG-FE-MN(380) ALUMINUM DIE-CASTING ALLOY

The microstructure of aluminium alloys based on 380 die-casting alloy was studied in detail, as a function of the alloying elements iron, ma gnesium, copper and manganese, and the solidification rate. Three meth ods of solidification were employed to simulate cooling rates obtained from investment, permanent, and die-casting processes, corresponding to similar to 0.4, similar to 12 and similar to 260 degrees C s(-1), r espectively, with emphasis on the highest cooling rate. Hardness measu rements were carried out on samples obtained from the latter, in the a s-cast and T5 tempered conditions (4 h at 25, 155, 180, 200 and 220 de grees C). The results have been discussed and the correlation between the hardness and microstructure as a function of alloying elements is presented. The effect of solution heat treatment on the variations in the microstructure and hardness has also been discussed.