A composite powder with a fine homogeneous distribution of the reinforcement phase in the whole particle can be obtained by mechanical alloying. Aluminium PM6061 unreinforced, and matrix composite reinforced with Si 3 N 4 and AlN powder, are milled in a high-energy attritor mill and the powder properties are compared with those of the same composite composition mixed in a horizontal low-energy ball mill. The correlation observed between the apparent densities and the milling time, explained by the morphological and microstructural evolution of the powder particles during the high-energy milling process, is used to determine the steady state of the process. At short milling times, the apparent density decreases as the milling time is extended, due to the deformation dominant at this stage; at longer milling times, it starts to increase with increasing milling time due to the piling up of the flattened particles and fracture of the welded particles. When mechanical alloying reaches the steady state, the apparent density is stabilized. A simple model is proposed to illustrate the mechanical alloying of a ductile–brittle component system. The particle size distribution and the microhardness of the mechanically alloyed particles are determined.

Effect of mechanical alloying on the morphology, microstructure and properties of aluminium matrix composite powders

In this paper, an Al6061–10 wt% SiC composite was prepared using the mechanical alloying route. The morphology and the structure of the prepared powder, which change with milling time, were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, respectively. Moreover, the relationships among the stages of mechanical alloying (MA), relative density and hardness of both pressed and hot extruded materials were investigated. The morphological evolutions showed that relatively equiaxed powders could be synthesized after 9 h of milling. The evolution of relative density and hardness with milling time is due to the morphological and microstructural changes imposed on the composite powder. High-relative densities are typical of the hot extruded samples. The effect of mechanical alloying process on hardness is more significant compared to reinforcement particles. The aging behaviors of the mechanically alloyed, commercially mixed and unreinforced Al6061 were compared. The results showed that MA composites exhibit no aging-hardenability.

Preparation and mechanical properties of SiC-reinforced Al6061 composite by mechanical alloying

Experimental evaluation of the influence of processing parameters on the mechanical properties of SiC particle reinforced AA6061 aluminium alloy matrix composite by powder processing

Modeling the influence of a process control agent on the properties of metal matrix composite powders using artificial neural networks

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=6269&context=eispapers

Mechanical properties and tribological behavior of aluminum matrix composites reinforced with in-situ AlB2 particles

The machining difficulties and processing costs related to particle reinforced aluminium matrix composites have limited the application range of these advanced materials. The present investigation deals with the production of net shape SiC particle reinforced AA6061 aluminium alloy components by a conventional powder metallurgical processing technique, involving the uniaxial cold pressing and sintering of composite powders. Three aluminium alloy powder sizes were combined with three SiC particle sizes in various volume fractions of up to 20% SiC, and processed to produce net shape tensile test samples. The tensile test results and the morphological analysis of the fracture surfaces show that this process may be used to produce well sintered, small-to-medium sized net shape aluminium composite components exhibiting ultimate tensile strength (UTS) of up to 324 MPa. The successful production of these aluminium powder based components is affected strongly by the aluminium powder size, SiC volume fraction and the SiC particle size. It is also linked to the penetration of the aluminium powder oxide layer by the hard SiC particles, which occurs during cold compaction. Based on the present investigations, a number of processing improvements are suggested, which should further advance the usefulness of this technically uncomplicated net shape processing method for the production of aluminium matrix composites.

G. O'Donnell

Papers

Production of aluminium matrix composite components using conventional PM technology