A study of thermal expansion of Al–Mg alloy composites containing fly ash

The coefficient of thermal expansion (CTE) of stir cast Al–Mg alloy A535 and its composites reinforced with a mixture of 5 wt.% fly ash and 5 wt.% silicon carbide, 10 wt.% and 15 wt.% fly ash particles was investigated using thermomechanical analysis (TMA). Micromechnical models proposed by Turner, Kerner and Schapery as well as the rule of mixture (ROM) were employed to compute the CTEs of the composites within the same temperature range. Experimental results showed that the CTE of A535 decreased with the addition of fly ash and SiC particles. Subjecting the test samples to a second re-heat cycle also affected their CTE response. The CTE obtained for A535 during the first heating cycle was higher than that obtained during the re-heat cycle whereas the reverse result was obtained for the fly ash composites. Furthermore, the analytical models could not predict the experimental CTEs the composites due to complexities arising from the presence of porosities, reaction products and other defects.

► Fly ash is potentially an inexpensive reinforcement material for aluminium alloys.
► Addition of fly ash into A535 aluminium alloy lowers its CTE.
► The presence of voids in the composites affected their CTE.
► SiC has a greater impact on CTE reduction than fly ash.
► The existing micromechanical models were not able to predict the CTE of fly ash-reinforced composites.