Al Matrix Composites Reinforced By Stirring Reaction Synthetical Al-Fe Intermetallics

The development of adscititious particle reinforced aluminium matrix composites and Al matrix in-situ composites reinforced by reaction synthesis' reinforcement phase are reviewed at first. And the papers point out the difficulties and problems on the study of Al matrix composites at present. Based on the literature analysis of Al matrix in-situ composites by reaction synthesis, it is found that in-situ reaction synthesis processed can ameliorate wettability between reinforcement phase and Al matrix alloys and strengthen interfacial bonding and improve mechanical properties of Al matrix composites. Then, the fabrication of Al3Fe(p)/Al composites and Al3Fe(p)+Al2O3(p)/Al composites by stirring casting and the development of this type of new materials are studied by the number.The reaction dynamics and thermodynamics analysis on the reaction systems of 3Al(l)+Fe(s)→Al3Fe(s) and 8Al(l)+Fe2O3(s)→Al2O3(s)+2Al3Fe(s) shows that the fabrication of those two kinds of composites are feasible in theory. Papers also points out that the size of the adscititious powder agglomerate enwrapped by pure Al melt, the effect and intensity of stirring shear force and the melt temperature at the beginning of reaction between the adscititious powder and Al melt are the main factors affecting the in-situ reaction ongoing velocity. In which, the size of the adscititious powder agglomerate enwrapped by pure Al melt is the foremost influencing factor. And bigger power agglomerates are enwrapped in Al melt, more time is needed to finishing the in-situ reaction. Because of the assemble-ease characteristic of oxide, the adscititious powder agglomerates added into Al melt have a bigger size and need more time to finishing the in-situ reaction in mixing melt. These analysis are proved by investigation is right.A set of special stirring equipment for stirring casting is designed, which can disperse evenly the powder and the reaction synthetical intermetallic reinforcement phase particles in pure Al melts. And a process of Al-Fe in-situ reaction synthetical Al matrix by stirring casting method is studied and established. The characteristic of stirring equipment is used a shaking sieve to disperse the adding pure Fe or Fe203 powder and used a combined stirrer instead of a common paddle stirrer to improve the shear effect to mixing melts. The particularity of fabricating process is the step of holding stirring at a constant high temperature. Both of which can improve the evendistributing degree of reinforcement phase in pure Al matrix.Based on the analytical result of stirring kinetics, the maximal affecting factors to the size and distribution homogeneous degree of intermetallic Al3Fe reinforcement phase in Al matrix during the stage of heat preservation stirring are studied, and some important parameters of stirring equipment and stirring process are ascertained, and the stirring processing is optimized. Using the special stirring equipment and the optimized stirring processing, some semi-solid Al matrix in-situ composites slurry with small size of Al3Fe reinforcement phase and even distribution of reinforcement particles in mixing melts are achieved.Used solid-liquid reaction synthesis technology and stirring casting and metal mold chilling processing, Al3Fe particles and Al3Fe+Al2O3 particles reinforced pure Al matrix in-situ composites are fabricated. The metallography analysis shows that the intermetallic Al3Fe exhibits two kinds of crystalline state-primary crystal Al3Fe and eutectic crystal Al3Fe-in Al + Fe reaction synthetical Al matrix in-situ composites. The eutectic crystal Al3Fe often is "needle" shape or short line shape but the shape of primary crystal Al3Fe is relative to the adding amount of Fe powder and the temperature of heat preservation stirring. While the adding amount of pure Fe powder is few and the temperature of heat preservation stirring is higher than the temperature of liquidus of Al-Fe binary alloys equilibrium phase diagram, the reaction synthetical primary crystal Al3Fe exhibits short worm shape. Wh...