the al-mg-si a6063 alloy reinforced with alumina short fibers has been diffusion-bonded with the bond interface perpendicular to the direction of the fibers, i. e. , the direction of the highest strength, and the effects of surface treatments, bonding parameters (temperature and pressure) and insert metals on the bond strength have been systematically investigated. the surface treatments used were (i) electropolishing, (ii) turning in a lathe and (iii) wire brushing. on the faying surface finished by (i), fibers protruding from the surface of the matrix metal were observed, and their height increased with electropolishing time. treatment (i) resulted in a bond strength considerably higher than those from (ii) and (iii), though the bond strength decreased with an increase in the protruding height of fibers of more than 8 $mu$ m. this decrease in the bond strength was probably due to the suppression of intimate contact between matrix surfaces by protruding fibers which were broken by the bonding pressure and laid on the bond interface. (edited author abstract) 20 refs