A Comparative Study of Porosity and Pore Morphology in a Directionally Solidified A356 Alloy

Abstract It is well-known that the better the control of the liquid aluminium allows obtaining of better properties. One of the most important defects that is held responsible for lower properties has been the presence of porosity. Porosity has always been associated with the amount of dissolved hydrogen in the liquid. However, it was shown that hydrogen was not the major source but only a contributor the porosity. The most important defect that causes porosity is the presence of bifilms. These defects are surface entrained mainly due to turbulence and uncontrolled melt transfer. In this work, a cylindrical mould was designed (Ø30 x 300 mm) both from sand and die. Moulds were produced both from sand and die. Water cooled copper chill was placed at the bottom of the mould in order to generate a directional solidification. After the melt was prepared, prior to casting of the DC cast samples, reduced pressure test sample was taken to measure the melt quality (i.e. bifilm index). The cast parts were then sectioned into regions and longitudinal and transverse areas were investigated metallographically. Pore size, shape and distribution was measured by image analysis. The formation of porosity was evaluated by means of bifilm content, size and distribution in A356 alloy.

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A Comparative Study on the Wear Behavior of Cast and Forge Aged A356 Alloy with Addition of Grain Refiner and/or Modifier

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.592-594.1255 ◽

2014 ◽

Vol 592-594 ◽

pp. 1255-1261 ◽

Cited By ~ 1

Author(s):

D.G. Mallapur ◽

D.G. Sondur ◽

K.R. Udupa

Keyword(s):

Comparative Study ◽

Wear Mechanism ◽

Wear Behavior ◽

Testing Machine ◽

A356 Alloy ◽

Wear Testing ◽

Unexpected Result ◽

Wear Properties ◽

Grain Refiner ◽

Aged Material

In the present work, a comparative study on the wear behavior of cast aged and forge aged A356 alloy has been investigated without and with the addition of grain refiner and modifier, under dry sliding conditions using a pin-on-disc wear testing machine. The comparison study reveals that tribological properties of A356 materials are highly influenced by T6 heat treatment process. It is found in the present study that, cast aged A356 materials possess higher wear resistance as compared to forge aged materials. Apart from this, the study also reveals that cast aged material is associated with lower frictional forces and coefficient of friction as compared to the forge aged category. It is further observed in the present investigation that abrasive wear mechanism is operative in both the categories of the materials when tested with lower load for lower sliding speed and lower distance of run. At higher values of external parameters the adhesive wear mechanism dominates the wear process. Lower values of wear properties recorded by the forge aged material are an unexpected result in the present studies. It is conceived to be due to the presence of micro cracks while forging.

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