Study On Ultrasonic Assisted Casting Al-Cr/Al In-situ Compsites

The aluminum matrix composite material have draw so much attention of researchersbecause of its having a high specific strength and specific rigidity, and good high temperatureperformance and good damping properties, low coefficient of thermal expansion of superiorperformance. There are two categories method to fabricate aluminum matrix composites,forced to join and in-situ synthesise. In-situ aluminum matrix composites, enhanced phase andmatrix good combination, the interface is clean, non-polluting, the particle is relatively smalland solved the interfacial reaction between the particles and the matrix wettability and otherissues. In recent years, researchers are using high-energy ultrasound propagation in a metal oralloy melt will generate acoustic cavitation and acoustic streaming and other non-lineareffects, to achieve grain refinement, uniform structure and promote the reaction.Combine the high-energy ultrasound-assisted technology and in-situ reaction, used Cr andAl reaction generated intermetallic compound at high temperatures, which distributed inaluminum uniformly, to enhance the property of pure aluminum in this paper. Usingorthogonal designed experiment to explore the optimal process parameters for preparation ofAl-Cr intermetallic compound/Al in-situ composites. Analysising with SEM, XRD, EDS,testing mechanical properties (microhardness, wear resistance, compression properties, tensileproperties,bending properties), physical properties (damping) and chemical properties(corrosion resistance and high-temperature oxidation resistance) of the composites, and finalstudying on the mechanism of high-energy ultrasound assisted casting role and Al-Cr/Al-insitu composites reinforced role. Those following are conclusions:(1) Having successfully fabricated the Al-Cr/Al in-situ composites by ultrasonicvibration assisted casting method. Al-Cr intermetallic compounds were irregular polygonaland small, enhanced phase and matrix good combination, cleaning interface, distributedevenly in the matrix. The volume of enhance phase and distribution had a certain relationshipwith the Cr powder particle size, the most uniformity distribution of enhanced phase is75μmof the Cr particle size. Al-Cr intermetallic compound formate many types, Al and Cr firstlygenerated Al0.983Cr0.017, as the Cr content increased, higher Cr, Al proportion of compound would be generated, as the temperature elevated, there is conducive to a more stable, betterperformance of the compound generated, these intermetallic compounds expansion,eventually forming the mixing enhancement, and holding stationary atomic ratio of Al and Cr.Since the mixed phase with of different structure type and different volume, the compositematerial properties would be some difference.(2)The reinforcing effect of the Al-Cr intermetallic compound to Al is obvious, themechanical properties of the composite material (micro-hardness, wear resistance,compression performance), physical properties (damping) and chemical properties (corrosionresistancesex) have been largely improved, compared with commercially pure aluminum.Among of it, the micro-hardness of the composite material is improved2.4times, the wearresistance increased61.8times, the compressive strength δbcincreased3.1times,25.7timesincreased in damping, corrosion resistance is improved by2.2times. Because of brittle phasesynthesized, the intermetallic compound grains are not easy to slip, the tensile δband flexuralstrength δbbof the composite material reduced. The composites have good high temperatureoxidation resistance, consistent with pure aluminum.(3) When the high-energy ultrasound propagation in melt will produce a series ofsecondary effects, such as acoustic cavitation, acoustic streaming, and thermal effects. Effectof acoustic cavitation bubble crash instantly are able to generate104K high temperature andhigh pressure up to105MPa, accelerated the Al-Cr intermetallic compounds generate andgood combination, also refined the intermetallic compound gains. The melt macro flow can becaused by acoustic streaming, and also the more uniform distribution of the reinforcingparticles in the melt. The property of Al-Cr/Al in-situ composites have been enhanced, whichmainly presented by the Al-Cr intermetallic compounds enhanced, dislocation enhanced,interface enhanced and matrix enhanced several aspects.