The hardness model was developed for aluminium metal matrix composites having Al7075 matrix reinforced with particles of Al 2 O 3 and fabricated by stir-casting. Four factors, five levels, central composite, rotatable design matrix was used to optimize the number of experiments. Adequacy of the model was tested by employing analysis of variance (ANOVA). The experimental results showed that size of reinforcement was the major parameter influencing the hardness of the composites among the other control factors, followed by weight fraction of reinforcement. However, the holding temperature and time had lower effects. The model suggests that one must take into account the interaction of parameters for predicting hardness of composites so that the optimal combination of the testing parameters could be determined and predicted.

Aluminium matrix based metal matrix composites (MMCs) are being extensively used in various industrial applications that need high strength combined with low weight, high hardness, wear resistance, high temperature resistance, improved impact strength, etc. They are amenable to secondary manufacturing processes such as extrusion, rolling, forging, welding, etc. However, because of their complex nature, both in terms of composition and difficulty in manufacturing by the standard fabrication techniques, researchers are keen to study various combinations of constituent materials -matrix and reinforcement, their processing, property evaluation, and extending their applications in various fields. This article presents the details of the investigation comprising stir casting of Al7075 matrix material reinforced with Al 2 O 3 particulates. An attempt has been made to predict the impact strength of these MMCs, which is an important property that decides their suitability in shock loading environment, both in the as-cast and forged conditions. Multi-factor, rotatable, central composite design has been used to predict the impact strength in terms of charpy-V. The mathematical models developed are validated using Fisher's F-test.

Introduction Monolithic alloys are slowly being replaced by composites, which combine ductility and toughness of the matrix materials and higher strength, hardness, wear resistance, etc. of the reinforcement materials. Metal Matrix Composites (MMCs) are being extensively used in automotive, aerospace and mining engineering, etc. as they are reported to possess high strength-to-weight ratio at elevated temperatures, improved shock-resistance properties, relatively higher wear resistance, toughness, etc [1][2][3][4][5][6]. In order to shape these composites, often they are subjected to secondary processing methods such as extrusion, rolling and forging. Consequently, MMCs having Al-7075 alloy as matrix and Al 2 O 3 reinforcements in the form of particulates are reported to exhibit improved mechanical properties such as high hardness, wear resistance, tensile strength, etc, not only in the as-cast condition, but also in the forged condition as well [7]. However, a deeper understanding of these alloys in respect of their production; mechanical/metallurgical properties is mandatory to enhance their applicability. Recently, factorial design of experiments has emerged as an important tool to analyze multi-parameter, complex processes [8][9][10][11]. A number of researchers have employed this methodology and developed mathematical models for various properties of MMCs [12][13][14][15][16][17][18][19][20][21]