HIGH MECHANICAL STRENGTH OF QUASI-CRYSTALLINE PHASE SURROUNDED BY FCC-AL PHASE IN RAPIDLY SOLIDIFIED AL-MN-CE ALLOYS

A nonequilibrium structure consisting of fine quasicrystalline (icosahedral) grains surrounded by fcc-Al phase was found to form in rapidly solidified Al-Mn-Ce alloys. The formation of the nonequilibrium structure is limited to a composition range of 4 to 6 at% Mn and 2 to 3% Ce which is located around the phase boundary between fcc solid solution and icosahedral plus amorphous phases. The icosahedral phase consists of equiaxed grains with a size of 50 to 100 nm and the width of the fcc-Al phase along the grain boundary is as small as 5 to 15 nm. The mixed phase alloys have good bending ductility and exhibit high tensile fracture strength (sigma(f)) of 960 to 1320 MPa. It should be noticed that the high sigma(f) values exceeding 1000 MPa are obtained for the Al-rich alloys containing the quasicrystalline phase. It is thus concluded that the lanthanide (Ce) element has a useful effect on the achievement of high mechanical strengths and good ductility through a significant structural modification resulting from the increase in the quenching effect.