Effect of IRON Removal on the Structure and Mecahnical Properties of Aluminium-Silicon Alloys
The research work examined the effect of the removal of iron from aluminium-silicon alloys using dopants on the structure and mechanical properties. Manganese, cobalt and molybdenum were used as the modifying elements. The as-cast Al Si alloys were analyzed for iron content using Atomic Absorption Spectrometer (AAS) technique. The dopants or modifying elements were added as micro additives at various compositions to the percentage of iron present in the master alloys. The modified alloys were produced by melting a calculated mass of the master alloys and adding the dopants in the ratios of 1:1, 2:1, 3:1 and 4.1 to the percentage of iron in the Al Si alloy. The properties tested were ultimate tensile strength, percentage elongation, hardness and microstructure. The result of the chemical analysis of the alloys indicated that the dopants were able to reduce the percentage of iron in the alloys. On addition of 5.4%Co iron was reduced from 1.8% to 0.42%, which is far less than the critical iron level of 0.78%. The mechanical tests showed an improvement with the highest values achieved by the addition of 5.4%Co. The improvement in the microstructure is also shown in plates 1-8.
CURRENT TECHNOLOGIES FOR THE REMOVAL OF IRON FROM ALUMINUM ALLOYS
In the current paper, the Fe-rich phases in and their detrimental effect on aluminum alloys are summarized. The existence of brittle platelet s-Fe-rich phases lowers the mechanical properties of aluminum alloys. The methods to neutralize the detrimental effect of iron are discussed. The use of high cooling rate, solution heat treatment and addition of elements such as Mn, Cr, Be, Co, Mo, Ni, V, W, Cu, Sr, or the rare earth elements Y, Nd, La and Ce are reported to modify the platelet Fe-rich phases in aluminum alloys. The mechanism of the modification is briefly described. Technologies to remove iron from aluminum are extensively reviewed. The precipitation and removal of Fe-rich phases (sludge) are discussed. The dense phases can be removed by methods such as gravitational separation, electromagnetic separation, and centrifuge. Other methods include electrolysis, electro-slag refining, fractional solidification, and fluxing refining. The expensive three-layer cell electrolysis process is the most successful technique to remove iron from aluminum so far.
The formation of β-FeSiAl5 and BeFe phases in Al7Si0.3Mg alloy containing Be
Thermal analysis and interrupted quench experiments have been carried out to study the formation of beta-FeSiAl5 and (Be-Fe)-BeSiFe2Al8 phases in Al-7Si-0.3Mg alloy with and without Be addition. In the base alloy with 0.6% Fe (without Be addition), a needle- and plate-shaped beta-phase is present in the interdendritic regions and is formed by a ternary eutectic reaction. In the Be- added alloy with 0.6% Fe, a Be-Fe phase of Chinese script and polygon shapes grows along with the primary alpha-Al dendrites, leading to superior mechanical properties. It is proposed that this Be-Fe phase is formed by a peritectic reaction. Be addition has also resulted in some grain refinement.