Study On Process Of Preparing A12o3/a1 By The Pressureless Infiltration Technique

The process for fabricating A12O3/A1 composites by the pressureless infiltration technique was studied on basis of the theory of physical pressureless infiltration technique and the preliminary discuss of the ways of determining porosity ratio of alumina preform. Advantages and disadvantages of three different processes, pouring directly, laying alloy on preform and pressing preform into alloy, were also analyzed by comparing their processes. The best experimental scheme of influences of infiltration depth was gained by means of orthogonal-design experiments and the effects of factors including the particle size of alumina, the amount of addition, infiltration temperature and the heat preservation time, on the infiltration depth of composites were analyzed. The micrographic structure and phase composition, as well as the thermodynamics and kinetics of the chemical reaction on the interface between alumina and aluminium alloy were all investigated through XRD, SEM, optical microscope, spectra instrument, etc. The results are listed as follows:I.It is better to determine porosity ratio of alumna preform by the means of kerosene infiltration than by the means of in the boiled water, and the experimental porosity ratio is basically close to the theoretical value.2.1t is found that the open porosity ratio of the preform reinforced by 6 u m particles of alumina is lower than that of other particles of alumina. Low open porosity can be obtained when alumina particular is close to round and smooth. The open porosity ratio decrease with the increase of pressing pressure of the preform.3.The mixture of Ti, Mg and NaHCOa are agreed to the desirable chemical wetting agents through optimal tests by the means of pouring directly and the results show thatthe best technological scheme is as follows: 6 u m A12O3 particle, 2wt% of Ti, 820癈 of infiltration temperature, three hour heat preservation time. The influencing degree of infiltration depth is ordinally heat preservation time, size of A12O3 particle, infiltration temperature, and the percentage of Ti.4.Desirable infiltration results can be obtained to fabricate A12O3/A1 composite by means of both laying alloy on perform and pressing preform into alloy. It is indicated that the A12O3 film can be removed when some A12 (SO4) 3 powder is added on the preform and that the composites will have better density and stronger connection of interface when it is protected by nitrogen during the infiltration process.5.By analyzing and comparing processes of pouring directly, laying alloy on preform and pressing perform into alloy, it is concluded that fabricating composites by means of laying alloy on preform is more convenient and feasible. But some technological measuresmust be taken to eliminate A12O3 film formed on surface of the aluminium alloy.6. A formula about the connection of the infiltration depth (H), capillarity pressure (Po), the heat preservation time (?) and the counter pressure in the preform (P\) wasdeduced as . Infiltration depth of composites increase with increase of capillarity pressure, the heat preservation time and decrease of the counter pressure in the preform.