The influence of casting methods on the surface microhardness and crystalline formation of aluminum-copper alloys.

The influence of air/gas, oxygen/gas, and electric casting methods on the surface microhardness and crystalline formation of three aluminum-copper alloys was verified. The inclusion, wax elimination, and casting of the pattern were accomplished by using conventional techniques for thermal expansion investment. After metalographic polishing, the surface hardness analysis was verified with a penetrator. The penetrations were transformed in Knoop hardness with the conversion table, and computed by variance analysis. The test sample surfaces were then etched with a reactive solution composed of equal parts of hydrogen peroxide and ammonium hydroxide. The crystalline grains precipitated by solution were photographed with Kodak film 32 ASA. The results demonstrated that the surface microhardness of the alloys was modified according to the heat sources used, and the crystalline grain disposition was also adversely influenced by the heat sources, with the exception of Goldent alloy.