The present dissertation is aimed at investigating the effects of additives on the mechanical properties and machinability of the 220 alloy which is a new Al-2%Cu-1.3%Si-0.4%Mg casting alloy intended for automotive applications. The research involved here was accomplished through two types of study: (i) study of mechanical properties; (ii) and study of machinability. The study of mechanical properties was proposed to examine the effects of Sr, Ti, Zr, Fe, Mn, and Ag as well as of free-cutting elements, specifically Sn and Bi, on the mechanical properties of the 220 alloy in both the as-cast and heat-treated conditions. The mechanical properties in question include tensile, hardness, and impact properties which were all evaluated at room temperature. The study of machinability was devoted to examining the drilling and tapping performance of four 220 based-alloys as well as of A206 alloy which was selected for a comparative study on the machinability of this particular alloy and that of 220 alloy. The four 220 based-alloys were selected from amongst the alloys prepared in the first study and include: (i) 220 alloy; (ii) 220 alloy + Ti + Zr; (iii) 220 alloy + Ti + Zr + Sn; and (iv) 220 alloy + Ti + Zr + Bi. The machining performance was evaluated based on the calculation of the cutting force, cutting moment, and tool life, as well as on the investigation of chip characteristics. Tool life was expressed as the number of holes drilled/tapped up to the point of tool breakage.An assessment of the microstructure reveals that A^Cu, AlsMggSiôC^, and the Chinese script-like a-Ali5(Fe,Mn)3Si2 phases are the main microstructural constituents of the 220 alloy. The absence of free Si in the microstructure implies that the Si-content was consumed in the formation of the Al-Fe-Si and Al-Cu-Mg-Si intermetallic phases. The platelet-like /?-AlsFeSi phase was not in evidence because of the higher Mn:Fe ratio (~1) of the 220 alloy which promotes the formation of the a-Fe phase at the expense of the /?-Fe phase. The addition of Sr refines the morphology of the ct-Fe Chinese script phase to a certain extent, resulting in the even distribution of the particles of this phase within the aluminum matrix. The combined addition of Ti and Zr causes a reduction in the grain size by about 68% compared to the non-grain-refined base 220 alloy. This reduction may be ascribed to the formation of Zr-Ti particles which act as nucleation sites for small equiaxed grains of cc-Al. Tin precipitates in the form of /?-Sn particles which appear as small non-uniformly distributed clusters usually solidified within the AbCu phase network. Bismuth and /?-Sn particles were found undissolved in the Almatrix after heat treatment, thereby making it possible to induce their free-cutting action during machining.Results from the evaluation of the mechanical properties show that, because of the low Si content, the effects of Sr on the mechanical properties with respect to the modification of silicon eutectic do not come into play. The role of Sr in refining th...
