Pit Morphology of Aluminum Alloy and Silicon Carbide/Aluminum Alloy Metal Matrix Composites
01 May 1990-Corrosion (Allen Press)-Vol. 46, Iss: 5, pp 402-409
TL;DR: Pit morphology of Al 5456, Al 6061, SiCw/Al 5456 (UNS A95456), Al 60 61 (UNs A96061) and SiCws/Al 6061 is studied in this article, in order to compare pitting processes of Si cw/al matrix composites with that of corresponding unreinforced alloys.
Abstract: Pit morphology of Al 5456 (UNS A95456), Al 6061 (UNS A96061), SiCw/Al 5456, and SiCw/Al 6061 is studied in order to compare pitting processes of SiCw/Al metal matrix composites with that of corresponding unreinforced alloys. Work on anodized samples of Al 6061 and SiCw/Al 6061 is also included. Pits on the composites are significantly more numerous, shallow, and widespread than on the monolithic materials. Studies of pit structure suggest there are two stages in pit development. The first involves the initial dissolution of metal atoms and opening of the pit, and the second involves pit enlargement or growth. For both materials, pits initiate at secondary particles within the metal matrix. In the case of Al 5456 and SiCw/Al 5456, it is shown that these particles are intermetallic phases composed of alloying elements Mg, Cr, Mn, and Al, as well as, Fe, which is an impurity of the metal. Under equivalent conditions of preparation and processing, a greater number of intermetallic phases form in the ...
•02 Aug 1972
TL;DR: In this article, important techniques to process metal matrix composites are described, then the interface region and its characteristics, properties of different metal matrix composite composites, and finally, the authors summarize different applications of metal matrices composites.
Abstract: Metal matrix composites consist of a metal or an alloy as the continuous matrix and a reinforcement that can be particle, short fiber or whisker, or continuous fiber. In this chapter, we first describe important techniques to process metal matrix composites, then we describe the interface region and its characteristics, properties of different metal matrix composites, and finally, we summarize different applications of metal matrix composites.
TL;DR: In this paper, the corrosion of metal matrix composites (MMCs) is reviewed with emphasis on relating MMC corrosion behaviour to the electrochemical and chemical properties of MMC constituents.
Abstract: The corrosion of metal matrix composites (MMCs) is reviewed with emphasis on relating MMC corrosion behaviour to the electrochemical and chemical properties of MMC constituents. Galvanic corrosion between the reinforcement constituent and the metal matrix governs the corrosion behaviour of many MMCs. Other factors such as residual contaminants of MMC processing and the formation of interphases between reinforcement and matrix can also have pronounced effects on MMC corrosion behaviour. The lack of inherent resistance to corrosion of some MMCs requires that they be coated with organic or inorganic coatings for protection. Although the ultimate goal is to engineer and design MMCs to have good inherent resistance to corrosion (while maintaining excellent mechanical properties), no significant breakthroughs have been achieved in this area for MMCs that are typically prone to corrosion (e.g. graphite-aluminium MMCs). In this review, aluminium, magnesium, lead, depleted uranium, and stainless steel MMCs...
TL;DR: In this article, the effect of the size and volume fraction of SiC particulates on the microstructural and corrosion behavior of Al/SiC metal matrix composites (MMCs) was studied.
Abstract: Several Al/SiC MMCs having several volume fractions up to 15 vol.% and different SiC particulates average sizes, typically, 11, 6 and 3 μm were fabricated using conventional powder metallurgy (PM) route. The effect of the size and volume fraction of SiC particulates on the microstructural and corrosion behavior of Al/SiC metal matrix composites (MMCs) were studied. The results revealed that the Al/SiC MMCs exhibited higher density than pure Al matrix. The static immersion corrosion tests of Al/SiC MMCs in 3.5 wt.% NaCl aqueous solution at several temperatures showed that, at ambient temperature, the Al/SiC MMCs have better corrosion resistance than the pure Al matrix. Reducing the SiC particles size and/or increasing the volume fraction of the SiC particulates reduce(s) the corrosion rate of the Al/SiC MMCs. In contrast, the Al/SiC composites exhibited higher corrosion rates at 50 °C and 75 °C than the pure Al matrix.
TL;DR: In this paper, the pitting susceptibility of metal matrix composites based on aluminium (1050) reinforced with particulate silicon carbide has been examined using polarization in neutral 1N NaCl solution at 25 °C.
Abstract: The pitting susceptibility of metal matrix composites based on aluminium (1050) reinforced with particulate silicon carbide has been examined using polarization in neutral 1N NaCl solution at 25 °C. Various tests have been carried out to assess the effects of reinforcement particle size, particle volume fraction, internal stresses, reaction product at the particle/matrix interface and voids at the interface. It has been found that the MMCs show increased susceptibility to pitting attack compared with unreinforced alloys and that the major contribution to this enhanced attack arises from voids at the reinforcement/matrix interface. The voids may arise either as a result of poor bonding at the reinforcement/matrix interface or from the presence of cracked reinforcement particles.
TL;DR: In this article, an extensive presence of intermetallic phases was observed in the cast products, as a result of both the inoculation by K 2 TiF 6 and the intensive reactivity of the carbides with the molten matrix.
Abstract: In the present effort, Aluminium Matrix Composites (AMCs) were produced by the addition of submicron sized TiC and WC particles of low (up to 1.0 vol%) content into a melt of Al1050. Casting was assisted by the use of K 2 TiF 6 as a wetting agent and mechanical stirring to limit particle clustering. An extensive presence of intermetallic phases was observed in the cast products, as a result of both the inoculation by K 2 TiF 6 and the intensive – mainly due to the fine carbide particle size – reactivity of the carbides with the molten matrix. Particle distribution was reasonably uniform comprising both clusters and isolated particles. The intermetallic particle dispersion has changed the intended nature of the composites. Instead of one type of reinforcement, that of carbide particles, the aluminium matrix contained two main types of reinforcement: (a) in-situ intermetallic particles and (b) carbide nanoparticles, as such, or more often as clusters of remaining carbide nanocores and aluminide particles. The reinforced materials exhibited a notably improved sliding wear performance over that of the alloy owing to the beneficial effect of both the carbide and the intermetallic phase dispersion. A wear mechanism was formulated based on microstructural features of the wear surface (repeated “hill-valley” morphology, surface oxide layers, crack formation and grooving). Cyclic potentiodynamic polarization in Dilute Harrison’s Solution (DHS) revealed that the corrosion behaviour of the reinforced materials was mainly controlled by the corrosion of the alloy matrix. As such, the predominating form of corrosion was intergranular corrosion (IC) of Al associated with the presence of alloy matrix impurities. Carbide nanoparticles, aluminide phase associated with them and their Al-matrix remained essentially intact of corrosion. IC progress was often inhibited by the presence of clusters of aluminide and carbide particles.