No abstract

No abstract

No abstract

The present paper evaluates the solderability of three discontinuously reinforced aluminium matrix composites. The tested composites were an aluminium alloy of the 2000 series (AA2014) reinforced with different percentages of silicon carbide particles (6, 13, and 20 vol.-% respectively). A similar study was carried out on the unreinforced aluminium alloy for comparative purposes. Three low temperature filler alloys of the Zn–Al system were used for soldering. Drop formation tests were performed to evaluate the wettability of the molten filler alloys and sample joints (single overlap specimens) were produced to determine solder penetration in the joint clearance. Microstructural studies of the joints were carried out to determine the effects of the solid reinforcement particles on molten pool behaviour and solidification mechanisms.

The application of a surface coating on SiC particles is studied as an alternative means of solving problems of reactivity between SiC reinforcements and molten aluminium and problems of low wetting which limit the application of casting routes for fabrication of Al–SiCp composites. The selected active barrier was a ceramic composed of SiO2, which was generated by controlled oxidation of the SiC particles. The coating behaves as an active barrier, preventing a direct reaction between molten aluminium and SiC to form Al4C3 as the main degradation product. At the same time, the SiO2 provokes other interfacial reactions, which are responsible for an improvement in wetting behaviour. Composites were prepared by mixing and compacting SiC particles with Al powders followed by melting in a vacuum furnace, and varying the residence time. Transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and field emission TEM were employed as the main characterization techniques to study the interfacial reactions occurring between the barrier and the molten aluminium. These studies showed that the SiO2 coating behaves as an active barrier which reacts with the molten Al to form a glassy phase Al–Si–O. This compound underwent partial crystallization during the composite manufacture to form mullite. The formation of an outer crystalline layer, composed mainly of Al2O3, was also detected. Participation of other secondary interface reactions inside the active barrier was also identified by HREM techniques.