Cooling Rate, Hardness and Microstructure of Aluminum Cast Alloys

This experiment investigated the cooling curve behavior, hardness and microstructure of two aluminum alloys produced by casting process. There are Al-1.37Zn-1.19Si and Al-1.66Si-1.35Zn derived from melting and alloying a pure aluminum with ADC12 (Al-Si) ingot. Cooling curve recorded from both those two alloys with pouring temperature at 710 oC and the mold temperature kept constant at 220 oC. The result shows, a freezing range of Al-1.37Zn-1.19Si alloy is 643–348 oC and Al-1.66Si-1.35Zn alloy is 621–401 oC. Then cooling rate obtained for Al-1.37Zn-1.19Si is 55.56 oC/S, and Al-1.66Si-1.35Zn is 30.09 oC/S. TThe higher hardness is 40.42 BHN at Al 1.66 Si-1.35Zn, while the lower value is 34.62 BHN on Al-1,37Zn-1,19Si alloy. The hardness value found higher when cooling rate is shorted. The number of silicon present on microstructure is highest in Al-1.37Zn-1.19Si alloy but the hardness value decreases. This is caused by the distribution of the silicon content in the alloy is irregular. It was found that the solidification rate had an effect on hardness, where the freezing rate obtained a high hardness value.