Co-relation between mechanical properties and porosity in thick, thin and thinnest sections of stepped casted workpiece using A-356 Aluminum alloy

Abstract

Abstract A-356 aluminum alloy stepped casted workpiece were prepared with step casting technique was investigated for the mechanical properties and porosity defects using various gating elements (ingate/runner) profiles. Similarly, casted workpieces were produced using single and double gating elements with circular (vortex free), square and rectangular runner and ingate profiles. Hardness (HV) and ultimate tensile strength (UTS) of the thick section prepared from single circular runner/ingate system was more in comparison to thin and thinnest sections extracted at respective heights. Similarly, hardness and tensile strengths of thick specimen prepared from double ingate/runner having circular shape was found greater in comparison to thin and thinnest sections accordingly. SEM images depicted increase of porosity levels in thin and thinnest sections prepared from single or double within workpiece manufactured from circular runner & ingate arrangements respectively. In addition, X-ray diffraction results further revealed increase in crystallite size, hardness and tensile strength for specimens manufactured through circular profiled single or double runner/ingate arrangement. The prepared specimens also follow inverse Hall-Petch and D 2/%P statistical fit with p < 0.05 between hardness and crystallite size. Hence, the specimen with lower crystallite size or finer grains depicted attenuated mechanical properties due to higher porosity levels. In other words, D 2/%P index ratio value <1.40 (≥95% data points follows) exhibited reductions in mechanical properties accompanied by decreasing crystallite size and vise-versa. Moreover, double gating runner & ingate combination exhibited comparatively lesser pores relative to single gating design. Hence, this study suggests double runner & ingate arrangement accompanied with circular cross-section are appropriate for large size step castings or complicated geometries production in foundries.