Zn-Al Filler Metal Research Articles

Study of Brazeability of SiC<sub>P</sub>/A356 Composites and Aluminum Alloy Using Semisolid Metal with High Solid Fraction by Stirring

The semi-solid brazing process of SiCp/A356 composites and 2024 aluminum alloy using Zn-Al eutectic filler metal at 450 °C has been investigated. The two substrates and Zn-Al filler metal were heated up to the semisolid temperature range of Zn-Al filler metal by a resistance heating plate. In order to mix the filler metal with the base metal of both sides to be a single uniform joint, a stirrer was introduced into the weld seam. After stirring, specimens were sectioned for analysis of macro- and micro-structures along the weld region. The research shows that SiCp/A356 composites and aluminum can be joining by semisolid metal. It can be found that almost half of the oxide film on the surface of the base metal was disrupted and removed through the observation by SEM. The metallurgical bonds formed between the filler metal and the base materials on the interface of oxide had been disrupted. Moreover, the oxide film of surface of aluminum alloy was more thoroughly disrupted and removed than that of surface of composites with existing of SiC particle.

Semi-Solid Stirring Brazing of SiCp/A356 Composites and Aluminum Alloy in Air

The semi-solid brazing process of SiCp/A356 composites and aluminum alloy was investigated. The two substrates were heated up to the semisolid temperature range of Zn-Al filler metal in the joint region by a resistance heating plate. At this point a stirrer was introduced into the weld seam in order to mix filler metal and the two sides of substrates into a single uniform joint. After stirring, specimens were sectioned for analysis of macro- and micro-structures along the weld region. The research shows that SiCp/A356 composites and aluminum can be successfully joining with semi-solid filler metal. It can be found that most of the oxide film on the surface of the base metal was disrupted and removed through the observation by SEM. The metallurgical bonds formed between the filler metal and the base materials. Moreover, the oxide film of surface of aluminum alloy was more thoroughly disrupted and removed than that of surface of composites with existing of Sic particle. The joint microstructure with globular α-Al grain enclosed by rich-Zn phase can be obtained after stirring brazing.

Substrate oxide undermining by a Zn–Al alloy during wetting of alumina reinforced 6061 Al matrix composite

Abstract The process of wetting of Al 2 O 3p /6061Al substrate by Zn–Al filler metal in air was investigated. The filler was found to wet the substrate by undermining the oxide layer on the substrate. Dynamic observations of substrate oxide undermining, conducted using conventional illumination and recording, were correlated with post-cooling microscopy and analysis. The undermining mechanisms were discussed and the influences of temperature, surface roughness and gas evolution on the propagation of undermining were examined. The Zn–Al filler droplet exhibited excellent wettability to the Al 2 O 3p /6061Al substrate via undermining and it completely spread on the substrate in the end. Spreading of the filler was found to be rapid before the filler droplet was depleted, wherein the increase of the undermining region radius was a linear function of time. However, after the depletion of filler droplet, the spreading became significantly sluggish and negligible further undermining was observed. The current wetting system was non-reactive and the linear spreading was believed to be associated with the presence of a precursor film showing up ahead of the macroscopically observable spreading front. The undermining velocity at the ‘linear’ spreading stage was independent of the volume of the filler droplet, but increased linearly with temperature. The propagation of undermining was much rapider on the substrate with higher roughness and was encouraged by the escaping of gaseous products from the substrate.

Floating of SiC particles in a Zn–Al filler metal

Floating of SiC particles in a Zn–Al filler metal was investigated as functions of isothermal holding time, holding temperature, particle volume fraction and size. The floating distance increased with isothermal holding time until a stabilized condition was reached with all particles floating on the top of the melt. The floating distance increased significantly with increasing holding temperature and particle size and decreased with increasing particle volume fraction. The measured floating rates deviated significantly from those predicted by the modified Stokes’ law at relatively low holding temperatures, but the correspondence turned better with increasing holding temperature. Although the effect of particle volume fraction had been taken into account in the modified Stokes’ law, the correspondence was not good between the measured and the calculated values at various particle volume fractions. The measured floating rates which increased with particle size were much lower than the calculated values, particularly for large particle sizes.