Direct Metal Oxidation Of Al <sub> Prepared 2 </ Sub> O <sub> 3 </ Sub> / Al Composite Forming Technology

In this paper, Al₂O₃/Al composites was produced by the directedoxidation of molten aluminum alloys (DIMOX). The emphasis hasbeen placed on the afects of process parameters on the oxidation of Al-Mg-Si alloys and composites forming. Thermal dynatically andkineticly, the influences in the growth surface morpholgy and mi-crostructure of composites of SiO₂ coated on the initial growth surfacewere investigated; Othology test was introduced into the optimization of parameters such as temperature, supplied aluminum alloys contentand growth time ect.; Mathematical model of the near-surface massdiffusion transport was theorically constructed and then the intercon-nections were analyzed in details of the Mg vapor diffusion dynaticsand the high temperature gas flow with the growth of DIMOXAl₂O₃/Al composites.The results indicate that:(1) SiO₂ addition on the molten surface of Al-Mg-Si alloys e-liminates the inculation, accelerates growth rate promotes the near-planar growth surface and the homogenity of the microstructure ofAl₂O₃/Al composites. The growth kiedtics of aluminium alloys withSiO₂ addition is different from that without SiO₂ addition in essence,undergoing three stages: initial reaction of silica with molten alloys,oxidation structure formation, bulk oxidation.(2) Levels of SiO₂ addition is in limits. Out of this limits, effectsof SiO₂ will weaken and even disapear.(3)When ultropure alumina powerder taken as growth-perma-tion barrier, the efficiency of barrier largely depends on the ratio of a-lumina and silicate. Growth-permation barrier works well with ratioof (2～2. 5):1.(4)Orthology test shows that the optimal process parameters ofproducing Al₂O₃/Al composites is suppling pure aluminium, growingat 1250℃ for 40 hours. Alloys of low Mg, Si content largely short-ens the time of near surface melt reaching Al₂O₃-(Al, Mg) equilibri-um, growth rate increases with temperature and weight gains are lin-ear to time between 24 hours and 48 hours.(5) Gas phases distribute in certain structure over the growthsurface; Mg vapor, MgO boundery and oxygen in turn from thegrowth surface to atmosphere. Varions gas flows determine the oxi-dation conditions by changing gas phases distribution structure. Gasflow parallel to the growth direction result in the abnornal growth;gas flow perpendicular to the growth direction hinders the compositesformation.(6)When the mol fraction of oxygen Xo₂ over the growth surfaceup to 1, the composites growth is out of restriction of oxygen flux.