Characteristics of Oxide Layer Formed on the Aluminium (LM6) Alloy and Aluminium (ADC12) Alloy During In-Situ Melting

Abstract

In-situ melting, also known as an in-situ casting, is a new casting technique that reduces the formation of porosities in aluminium (Al) castings by removing the need for pouring. The melting phenomena of Al are influenced by its oxidation during in-situ melting. The purpose of this research is to find out how the oxide layer generated on the surface of Al alloy (LM6) and (ADC12) cubes during in-situ melting works. Al alloy cubes with approximate dimensions of (L: 1.0cm, W: 1.0cm, and H: 1.0cm) were inserted in a ceramic plate and heated for 30 minutes at 700°C and 750°C in a laboratory furnace. The heated samples were prepared for microstructure and elemental analysis using Optical Microscope (OM), Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Both Al alloys deformed from a solid uniform cube to a distorted shape after heating at temperatures of 700°C and 750°C while the colour changed from a shiny and silvery grey to dark grey. Al LM6 alloy cube changed from its shiny and silvery grey (raw sample) to dusty and dark grey mixed with buff (yellow-brown color) at 700°C, while at 750°C it turned to charcoal grey. For Al ADC 12 alloy sample, the colour changed from its shiny and silvery grey to slightly darker grey at 700°C and mixed with yellowish-grey color at 750°C. The colour changes indicating oxidation of the Al alloys cubes during in-situ melting had occurred, forming superficial layers of aluminium oxide Al2O3. XRD analysis revealed the oxide compounds on the surface of Al LM6 alloy cubes were complex oxide including Al2O3 hydroxide and spinel. While XRD analysis for Al ADC 12 alloy oxide after heating at the temperature of 750°C contains aluminium oxide hydroxide. It is considered that the aluminium alloy was transformed to the final or stable phase of aluminium oxide (Al2O3).