NEW AMORPHOUS-ALLOYS IN AL-MG-LN (LN=LA, CE OR ND) SYSTEMS PREPARED BY RAPID SOLIDIFICATION

New amorphous alloys were found to form at the high Al+Mg concentratio n of A1(50)Mg(44)Ln(6) (Ln=La, Ce or Nd) by rapid solidification. No a morphous phase is formed in Al-Mg binary system and hence the dissolut ion of a small amount of the Ln elements with large atomic radii of 0. 182 to 0.188 nn to Al-Mg binary alloy is concluded to be effective for the increase in the glass-forming ability. The effectiveness is mainl y due to the satisfaction of the criteria for the achievement of the l arge glass forming ability in the ternary alloy systems, i.e., the lar ge atomic size ratios of the constituent elements (Ln>Mg>Al) and large negative heats of mixing among the three elements. The importance of the atomic size ratio for the glass formation is also supported by the absence of an amorphous phase in the case of other Ln elements with a tomic sizes smaller than the Ln elements (La, Ce or Nd). The crystalli zation of these amorphous alloys takes place through the simultaneous precipitation of more than two kinds of compounds. The completion of t he crystallization by this precipitation mode allows us to infer that the simultaneous dissolution of the three elements plays an important role in the construction of the present new amorphous structure.