Microstructure and mechanical properties of Al/Al 2 O 3 MMC produced by anodising and cold roll bonding R. Jamaati* and M. R. Toroghinejad In the present paper, Al–Al 2 O 3 composite strips are produced by the cold roll bonding process of anodised aluminium strips. This technique has the flexibility to control the volume fraction of metal matrix composites by varying the oxide layer thickness on the anodised aluminium strip. Microhardness, tensile strength and elongation of composite strips are investigated as a function of quantity of alumina and the applied production method. It is found that higher quantities of alumina improve microhardness and tensile strength, while the elongation value decreases negligibly. Furthermore, prerolling annealing is found to be the best method of producing this composite via the cold roll bonding process. Finally, it is found that both monolithic aluminium and aluminium/alumina composite exhibited a ductile fracture, having dimples and shear zones. Keywords: Metal matrix composite, Cold roll bonding, Anodising, Microstructure, Mechanical properties Introduction There has been a wide interest in developing metal matrix composites (MMCs) due to their unique mechan- ical properties, such as light weight and high elastic modulus. The common fabrication routes of particulate reinforced MMCs include spray deposition, liquid metallurgy and powder metallurgy. 1,2 Since expensive equipment is required and the processing routes are usually complex, the high cost of producing MMCs using these methods has limited the application of MMC materials. Among the current composite material technologies, cold roll bonding (CRB) for producing composite sheets and foils has experienced rapid growth and development in recent years owing to its efficiency and economic considerations. Cold roll bonding is a solid phase welding process, in which bonding is established by joint plastic deformation of the metals to be bonded. Bonding is obtained when the surface expansion breaks the oxide layers, and the roll pressure bonds the surfaces together causing the material to be extruded through cracks in the fractured oxides, if present. 3–7 CRB is also referred to by different authors as ‘cold pressure welding by rolling’, 8 ‘bonding by cold rolling’, 9 ‘clad sheet by rolling’, 10 and cold roll bonding. 3–7 This process can be used with a large number of materials. In addition, materials that cannot be bonded by traditional fusion often respond well to CRB. Compared with other methods, CRB is of low cost and simple, and can be easily automated. To date, this method has been widely used for producing dissimilar layered composites, including Al– steel, 11 Al–Zn, 12 Al–Ti (Ref. 13) and Al–Ni. 14 In addi- tion, the authors have produced MMCs by continual annealing and roll bonding 15,16 and accumulative roll bonding 17,18 processes. These MMCs exhibited excellent microstructure and mechanical properties, but the production methods were costly. However, there is no conclusive research either on the production of MMCs with different quantities of reinforcement by anodising and CRB processes or on the effects of different annealing treatments (pre- and post-rolling) on the MMC micro- structure and mechanical properties. The aim of the present study was to manufacture the Al–Al 2 O 3 composite via anodising and CRB processes and to investigate the composite’s microstructure and mechanical properties, such as tensile strength and microhardness. In addition, the effects of pre- and post- rolling annealing treatments on microstructure and mechanical properties were examined. Experimental As received commercial purity aluminium sheets were cut into 20065060?4 mm strips parallel to the sheet rolling direction. Furthermore, some of the specimens were annealed at 643 K for 2 h (specifications are given in Table 1). Some of the as received and annealed strips were anodised in 15 wt-% sulphuric acid under an applied voltage of 16 V for two different times (5 and 60 min) to generate two extra oxide film thicknesses. Before anodising, the specimens were cleaned in NaOH and then in a HNO 3 bath. Chemical compositions of the baths are given in Table 2. To ensure a constant and homogeneous temperature throughout the solution, Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156–83111, Iran 26 August 2010 *Corresponding author, email r.jamaatikenari@ma.iut.ac.ir 1648 ß 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 26 August 2010; accepted 18 October 2010 DOI 10.1179/1743284710Y.0000000011 Materials Science and Technology 2011 VOL 27 NO 11