Effects of Magnesium on the Microstructure of Cast Aluminum Alloy Using Sand Casting Method

Abstract

In this study, the effects of magnesium (Mg) addition to aluminum (Al)
alloy at different percentage composition on the microstructure of this
alloy were examined. For this experimental study, the different alloys
of 4%, 8% and 14% by weight with various composition of magnesium
were prepared through casting process using sand casting method.
The sand casting method was employed in the casting process due to
its low cost of setting up and availability. The high reputation of AlMg (LM25) alloy in automotive industries stems from its light weight
(density), high strength to weight ratio, excellent casting
characteristics, high corrosion resistance, low coefficient of thermal
expansion, good thermal and electrical conductivity and good
mechanical properties including high machinability and workability.
The microstructure of this alloy depends strongly in its composition
and solidification rate. The specimens used for this research was
prepared using sand casting method. It was machined and grinded
using a series of silicon carbide paper and then polished using emery
paper. The emery paper is used to obtain a mirror finishing of the
surface of the specimens. The specimens were etched in an aqueous
solution of sodium hydroxide (Na0H) and was washed and rinsed with
alcohol and water. Various micrographs of the surface of the cast
specimen were taken with a light optical microscope with different
magnification in other to examine the surface finishing of the cast
specimens. This was done in the Engineering Management
Development Institute (EMDI) Akure, Ondo State. The 4% Mg in AlMg alloy consists of dendrites of aluminum and solid solutions as the
primary phase and eutectic mixture filling the interdendritic spaces.
The 8% Mg in A-Mg alloy shows the presence of eutectic magnesium
and the dendritic structure forms a network of dendrites all over the
surface, while the 14% Mg shows white fields which are primary
aluminum solid solution with a uniform distribution of magnesium,
this causes complete fusion with the primary aluminum grains. These
various attributes in the variation composition of Mg in Al-Mg alloy is
responsible for the formation of dendrites along the regions, it also
causes a decrease in the average value of the dendrite arm and grain
size; and these variations in Mg composition increases the mechanical
properties of the cast material.