Microstructure and Properties of Bulky Al84 Ni10 Ce6 Alloys with Amorphous Surface Layer Prepared by High-Pressure Die Casting

Abstract

An Al84 Ni10 Ce6 alloy surrounded by an amorphous surface layer has been formed in the sheet and cylinder samples with thicknesses of 0.5 to 5 mm by a high-pressure die casting process. The thickness of the amorphous surface layer in the region (A) which is away by 65 mm from the inlet gate of the mold is about 0.03 to 0.05 mm for the sheet with a thickness of 0.5 mm, about 0.10 to 0.16 mm for the cylinder with a diameter of 3 mm and about 0.18 to 0.20 mm for the 5 mm cylinder, though the amorphous layers for the 3 and 5 mm cylinders contain a small amount of crystalline phases. The increase in the thickness of the amorphous layer with increasing sample thickness is presumably due to the increase in the heat flow between the molten alloy and the copper mold through the increase in the effective applied pressure with increasing amount of molten alloy. There is a tendency for the thickness of the amorphous layer to decrease with decreasing distance from the inlet gate of the mold. The hardness and crystallization temperature for the amorphous layer in the 0.5 mm sheet are 370 and 556 K, respectively. The corrosion resistance against NaOH solution for the amorphous layer is much better than that for pure Al metal with the highest corrosion resistance in conventional Al-based alloys. The formation of the amorphous surface layer in the wide sample thickness range is important as one method which utilizes the features of Al-based amorphous alloys. © 1994, The Japan Institute of Metals. All rights reserved.