Experimental evaluation of the coefficient of thermal expansion of chilled aluminum alloy-borosilicate glass (P) composite

Aluminum metal matrix composites (AMCs) are fast emerging as the new generation material that are on a very brisk rate eliminating the use of conventional monolithic metals and alloys in aerospace, automobile and electronic-packing applications. Such, high technology applications calls for materials which possess near zero coefficient of thermal expansion (CTE) at higher operating temperatures. The paper investigates the coefficient of thermal expansion of the chilled LM-25 aluminum matrix composite reinforced with borosilicate glass powder. The composites are prepared via stir casting route by varying the weight percent (wt.%) of reinforcing particulates in the metal matrix starting from 3 wt.% and going up till 12 wt.% with an increment of 3wt.% in every step. In order to ensure sound, defect free castings, judicious use of two metallic and two nonmetallic end chills in a sand mold have been made. The CTE of the specimens drawn from the castings have been obtained. The analysis of the results illustrates a strong relationship between the CTE and wt.% reinforcement. It is also evident that different chill materials possessing different Volumetric Heat Capacities (VHC) also bear a strong effect not only on the quality of the castings produced but also on the CTE of the AMCs.