Abnormal thermal expansion behavior of aluminum borate whisker reinforced aluminum composite containing Fe₃O₄ particles

The thermal expansion behaviors of an aluminum matrix composite reinforced with aluminum borate whiskers and Fe₃O₄ particles were studied. The results indicated that the coefficient of thermal expansion (CTE) of this kind of composite was lower than that of the aluminum matrix composite reinforced with aluminum borate whisker. The CTE of the as-cast composite decreased with the increasing content of Fe₃O₄ particles. It was also found that there was a minimum of CTE in the temperature range from 200 to 400 °C for an as-cast composite with a higher volume fraction of Fe₃O₄ particles. However, after one thermal cycle between 30 and 450 °C, the minimum of CTE disappeared and the CTE of the composite became stable in the same temperature range. The results indicated that the abnormal thermal expansion behavior was resulted from the reduction of the partial oxidized Fe₃O₄ in the composite during the heating process.