The processing and characterization of sintered metal-reinforced aluminum matrix composites

Aluminum metal matrix composites are often reinforced with costly ceramic materials. However, porous sintered metal compacts can provide a low-cost alternative. The objective of this investigation was to produce and characterize sintered ferrous metal reinforced 380 aluminum alloy matrix composites, fabricated through a high-pressure casting technique. Tensile, compressive, and rolling contact fatigue tests were used to evaluate the composite properties.; During composite fabrication, a non-stoichiometric reaction phase, containing aluminum and iron, formed between the infiltrating molten aluminum and ferrous reinforcement. At high volume fractions, this reaction phase limited composite strength by promoting failure at low stress levels. To minimize the volume fraction of this reaction phase through rapid solidification, the optimum casting conditions were: a metal casting temperature of 675°C, a compact immersion duration of 30 seconds, a maximum punch velocity of 102 cm/min, and a maximum punch dwell pressure of 164 MPa.; Superior composite mechanical properties were produced when the compact consisted of relatively large particles (−80 mesh) that contained a sufficient amount of chromium as an alloying element to make the compact stainless. In addition, the strength of the compact and resulting composite was further improved through a high compact relative density and high quality interparticle bonding, which produced a high-strength reinforcing phase. Only the 409 stainless steel compacts exhibited all these properties, and as a result, produced superior composites. The remaining composite types exhibited limited ductility due to the reinforcing ferrous compact having a low relative density and poor interparticle bonding (Delcrome 6347 and HC_x) or from a high volume fraction of brittle reaction phase (Anchorsteel 1000).; In rolling contact fatigue, each composite type exhibited fatigue lives comparable to the unreinforced 380 aluminum alloy at the same nominal loads. However, when tested at the same normalized loads (applied load divided by the yield strength), only the 409 stainless steel composites exhibited consistently superior fatigue life. The comparatively high fatigue resistance of these composites was attributed to their ability to experience considerable ductility as a result of the properties of the 409 stainless steel compact.; Finite element analysis simulation of the tensile and rolling contact mechanical tests on the composite material demonstrated that the majority of the high stress is located in the ferrous reinforcing phase, with stress concentrations present at notches in the ferrous particles. However, high stresses are also generated in the aluminum matrix through elastic constraint. In rolling contact fatigue, these microstructural features can generate high stresses depending upon their orientation with respect to the maximum principal stress axis.