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H.-S.Chu et al./Seripta Materialia 45 (2001)541-546 545 6061 alloy 6061-10%Al203 ---6061-20%A1203 100150200250300350400450500 Temperature(C) Fig.5.DSC analysis of 6061 alloy and composites.Temperature range:100-450C and heating rate:10C/min. composites since B"zone is the only hardening precipitate in the 6061 alloy matrix. Suppression of the B"zone in composites was considered to be a result of the con- sumption of solute Mg by the formation of MgAl,O4. The tensile properties of composites Table 2 lists the tensile properties of the 6061 alloy and composites.Decreased yield strengths of composites are attributable to the consumption of Mg by the formation of MgAl,O4 as stated in the previous section.However,the composites exhibit a large work-hardening capacity,which is indicated by the large difference between the tensile strength and the yield strength.This difference is accredited to the large incompatibility in plastic deformation of the Al2O3 particles and the matrix [9].The composites also exhibit excellent ductility,and are far superior to the 6061-15 vol%(16 um)Al2O3 and 6061-15 vol%(16 um)SiC composites which have an elongation of 3-4%at a tensile strength about 340 MPa [9,12,13].This occurrence is believed to be due to a minimum of pores,particle clustering or poor interface bonding. Conclusions This work has demonstrated that 6061Al-0.3 um Al2O3p composites can be con- solidated and fully densified from powder compact by reciprocating extrusion.These submicron-sized Al2O3 particles can be dispersed uniformly in the matrix.The ag- ing responses of composites are much lower than that of the 6061 alloy.The DSC Table 2 The tensile properties of 6061 alloy and composites in the T6 condition Material Young's modulus(GPa)Yield strength(MPa) Tensile strength (MPa) Elongation(%) 6061 alloy 69 300 318 18.2 6061-10%Al20385 198 290 10.6 6061-20%Al20398 202 363 8.8 9 ! 9 / + +: 0 I + +: / # / 1 # / 5 / 0 5 6A7 0 # - D ; < - D ; < !" / :D : +3 6A##7 0 # 0 / 1 . / 0 9 0 / 0 I!" F - I!" 0 > :-" > "= 0 0 0 + ( L ;K3< ( ;+3< 0 ;+3< 4 ;D< A H H D H- AH A D AH HH &'& # &( ) *+ ,- ) ,.) / -:-