U.T.S. Pillai

A study of the influence of mischmetal additions to Al-7Si-0.3Mg (LM 25/356) alloy

This article deals with the effect of 0.25-1.5 wt pct mischmetal (MM) addition on the mechanical properties, microstructure, electrical conductivity, and fracture behavior of cast Al-7Si-0.3Mg (LM 25/356) alloy. Modification of eutectic silicon by MM is compared with strontium modification in terms of microstructure, mechanical properties, and fading behavior. Loss of magnesium encountered on holding the molten alloy and its resultant effect on mechanical properties of alloys modified with MM and Sr are compared with those in the unmodified alloy.

Fracture behaviour of pressure die-cast aluminium-graphite composites

Fracture toughness values of pressure die-cast Al-7Si-3 Mg-5 graphite composites were measured and found to be in the range 8–10 MPa m1/2. Detailed microstructure of the composite and the fractured surfaces were examined. Defects such as clusters, agglomerations and segregation of graphite particles, play a dominant role in accelerating the fracture process. In addition, the acicular silicon phase present in the matrix and the casting defects, such as gas and shrinkage porosities, also initiated and accelerated the crack, thus lowering the fracture toughness of the composites.

Pressure die cast graphite dispersed AlSiMg alloy matrix composites

Abstract An improvement in casting of aluminium alloy graphite particulate composite synthesized by stir casting is discussed. About 15 wt.% graphite particles were dispersed in AlSiMg (LM 25) alloy by the rheocasting technique. The composite ingots were used as a master alloy and diluted further with LM 25 alloy to obtain a 5 wt.% dispersion of graphite in the matrix. The composite ingots thus processed were subsequently remelted and pressure die cast into plates. Macroscopic and microscopic examination of the plates revealed fewer defects and a fine distribution of particles. The ultimate tensile strength evaluated in this composite was superior (132–136 MPa) to that of gravity die cast (85–95 MPa) composites. The fracture toughness of the composites was in the range 8–10 MPa m 1 2 .

LOW-PRESSURE CASTING OF LM25 (Al-7Si-0.3 Mg) ALUMINIUM ALLOY

ABSTRACT Low-pressure casting (LPC) is a specialized process for producing thin component castings of ferrous and nonferrous metals and alloys. This process has fewer casting and mold-filling problems than conventional processes like gravity and pressure-die casting, thus giving rise to castings with good mechanical properties. In the present study, LM25 (Al-7Si-0.3 Mg) aluminium alloy castings have been produced using indigenously designed and developed LPC setup. Using this process, defect-free, quality castings as well as thin castings of thickness down to 2 mm have been successfully cast. The strength properties of LP cast LM25 alloy are found to be higher than those of the gravity cast alloy. The microstructure of LPC aluminium alloy is seen with fewer casting defects and less porosity.