Abstract: With the increasing use of Aluminium foundry alloys for automotive and aerospace components the Aluminium industry has to focus sharply on the quality and reliability of such components. One of the biggest problems in Aluminium castings is porosity, caused mainly by solidification shrinkage and the evolution of dissolved gases. The presence of porosity is inevitable to a certain extent in any casting, can be very detrimental with respect to the mechanical properties. In general Aluminium alloys solidify over a wide temperature range, and therefore, their solidification mode is of the mushy type. Also, due to good thermal conductivity and high latent heat, it is difficult to maintain steep temperature gradients during casting solidification. When suitably designed, risers can eliminate macroporosity, but may not be effective in preventing microporosity formation in the inter dendritic regions. Other means such as chilling to establish favorable temperature gradients are required to achieve soundness.
In this project, the effects of casting design parameters i.e. section thickness, Taper, risers and chills on microshrinkage porosity and microstructure have been investigated experimentally in a wide freezing range Aluminium- 4.5% Copper alloy. Hollow cylindrical geometry castings, which are widely produced in automotive, aerospace and defence industries were sand cast under different designs. Cooling curves were recorded for different locations in the castings. Castings were subjected to X-ray radiography to evaluate internal soundness over the entire height. Castings were sectioned for density measurement and percent porosity values were calculated from the measured densities. Metallographic observations were carried out to characterize the type of microstructure, size and distribution of porosity. Results from the evaluations were compiled and correlated to the solidification parameters which, in turn were controlled by the casting design variables.

Key Words: Sand Casting, Aluminium Alloy, Cylindrical castings, Porosity.

| DOI: 10.17148/IARJSET.2021.8839