Journal of Materials Processing Technology 142 (2003) 738–743 Microstructure and interface characteristics of B 4 C, SiC and Al 2 O 3 reinforced Al matrix composites: a comparative study K.M. Shorowordi a , T. Laoui b , A.S.M.A. Haseeb a,∗ , J.P. Celis b , L. Froyen b a Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka 1000, Bangladesh b Department of Metallurgy and Materials Engineering, Catholic University of Leuven (KU Leuven), Kasteelpark Arenberg 44, Heverlee 3001, Belgium Received 21 November 2001; received in revised form 20 May 2003; accepted 5 June 2003 Abstract Three aluminium metal matrix composites containing reinforcing particles of B 4 C, SiC and Al 2 O 3 (0–20 vol.%) were processed. The stir-casting manufacturing route followed by hot extrusion was utilized, being one of the cost-effective industrial methods. A clear interfacial reaction product/layer was found at Al–SiC interface for composites held for a relatively long processing time (>30 min). No reaction product was observed at Al–B 4 C and Al–Al 2 O 3 interfaces at the resolution limit of the SEM used. On the other hand, two secondary phases (alumina and another phase containing aluminium, boron and carbon) were found in the aluminum matrix away from the interface in Al–B 4 C composites. From the fracture surface analysis, B 4 C reinforced Al composite seemed to exhibit a better interfacial bonding compared to the other two composites. © 2003 Elsevier B.V. All rights reserved. Keywords: Metal matrix composites; Stir casting; Interface; Secondary phase; Wetting 1. Introduction Aluminium metal matrix composites (Al MMCs) are be- ing considered as a group of new advanced materials for its light weight, high strength, high specific modulus, low co-efficient of thermal expansion and good wear resistance properties. Combination of these properties are not available in a conventional material [1]. The use of Al MMC has been limited in very specific applications such as aerospace and military weapon due to high processing cost. Recently, Al matrix composites have been used for the automobile prod- ucts such as engine piston, cylinder liner, brake disc/drum etc. [2]. Processing techniques for Al MMCs can be classi- fied into (1) liquid state processing, (2) semisolid processing and (3) powder metallurgy [3,4]. Particulate reinforced Al composites can be processed more easily by the liquid state i.e. melt-stirring process. Melt stir casting is an attractive processing method since it is relatively inexpensive and of- fers a wide selection of materials and processing conditions. The primary function of the reinforcement in MMCs is to carry most of the applied load, where the matrix binds the reinforcements together, and transmits and distributes ∗ Corresponding author. E-mail address: haseeb@mme.buet.ac.bd (A.S.M.A. Haseeb). the external loads to the individual reinforcement [5]. Good wetting is an essential condition for the generation of a satis- factory bond between particulate reinforcements and liquid Al metal matrix during casting composites, to allow transfer and distribution of load from the matrix to the reinforce- ments without failure. Strong bonds at the interface are re- quired for good wetting. These bonds may be formed by mutual dissolution or reaction of the particulates and matrix metal. The reaction phenomena are very detrimental to the composite as they bring about a decrease of the mechanical properties [6]. Substantial information is available in literatures on wet- ting and interface of Al-alloy MMCs reinforced with SiC, Al 2 O 3 particulates [7–13]. Al–SiC system is a reactive sys- tem, as it produces Al 4 SiC 4 or Al 4 C 3 compound at the in- terface of particles and metal [10,11]. Al 4 C 3 is detrimental for the composites properties. The formation of Al 4 C 3 can be minimized in several ways such as (1) using a suitable coating on particles, (2) using high silicon content Al alloys or (3) using pre-oxidized silicon carbide particulates [5]. The only reaction at the interface of Al–Al 2 O 3 composites is Al 2 O 3 dissolving into aluminium. Small addition of Mg encourages the formation of MgAl 2 O 4 spinal with Al 2 O 3 . Some studies on the reactivity B 4 C in aluminium processed by infiltration and powder metallurgy techniques reported the formation of different compounds at different processing 0924-0136/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0924-0136(03)00815-X