Active-Transient Liquid Phase (A-TLP) Bonding of Pure Aluminum Matrix Composite Reinforced with Short Alumina Fiber Usin
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TRODUCTION
ALTHOUGH the addition of discontinuous ceramic reinforcement into an aluminum matrix can improve the stiffness, wear resistance, and compressive strength at an elevated temperature of monolithic aluminum matrix, the presence of ceramic reinforcement in aluminum metal matrix composites (Al-MMCs) deteriorates the weldability primarily because of the intense and detrimental interfacial reaction between ceramic particles and superheated Al melt in arc welding.[1–4] Thus, friction-stir welding and brazing are promising methods for joining discontinuously reinforced Al-MMCs.[5–7] Because both Al matrix and ceramic particles coexist on the surface of Al-MMCs to be joined,[8] the brazeability of Al-MMCs is determined by the wettability at two kinds of microinterfaces: matrix/brazing filler metal (M/ M) and reinforcement/brazing filler metal (R/M).[7] GUIFENG ZHANG, Associate Professor, and WEI SU, Graduate Student, are with the State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, P.R. China. Contact e-mail: [email protected]. AKIO SUZUMURA, Professor, is with the Department of Mechanical and Aerospace System Engineering, Tokyo Institute of Technology, Tokyo 152-8552, Japan. Manuscript submitted July 26, 2014 Article published online February 10, 2016. 2026—VOLUME 47B, JUNE 2016
The first factor governing the wettability at both M/M and R/M interfaces is the composition design of the brazing filler metal. The published brazing filler metals can be classified into three groups with different melting regions: (I) Zn-Al(-Cu),[9–12] (II) Al-12Si (4047),[13,14] and Al-11.6Si-1.5Mg [4N04 with a melting range of 840 K to 850 K (567 C to 577 C)] systems,[7,8,14–17] and (III) Al-28Cu-5Si-2Mg with a melting range of 798 K to 808 K (525 C to 535 C)[18,19] and Al-24Cu-5Si-0.5Ni.[20] For Zn-based filler metals, flux (hygroscopic chlorides),[9] ultrasonic vibration,[10,11] or stirring[12] must be introduced to remove oxide film on the Al matrix surface at a lower joining temperature in air. For Al-Si brazing filler metal, an interfacial gap (1 lm) at R/M interface was observed,[13] and it was easy to discharge from the joint interface under pressure, leading to the lack of dissolution of Al matrix. For Al-Si-Mg brazing filler metal, Suzumura et al. first demonstrated that Al-12Si-1.5Mg filler metal could spread on the surface of Al matrix composite reinforced by a short alumina fiber while Al-12Si remained in the original shape of wire in the wettability test in a vacuum.[14] Moreover, although Al-12Si-1.5Mg brazing filler metal was able to wet Al matrix with rougher surface[14] and the interface void can be eliminated with appropriate pressure,[17] the poor wettability at the R/M interface led to a decrease in joint strength with increase METALLURGICAL AND MATERIALS TRANSACTIONS B
in volume fraction of reinforcement.[7,15] For Al-25Cu5Si-2Mg (wt pct) braze with a low melting range from 798 K (525 C) to 808 K (535 C), chloride flux (rather than fluoride flux) or relative high pressure
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