Effect of some manufacturing parameters on mechanical and machining characteristics of extruded (al – al2o3) composites

The fabrication, microstructure, mechanical properties and machinability of particulate metal matrix composite (Al / Al2O3) were investigated. The following conclusions have been drawn.FabricationRange of particulate metal matrix composites of (Al / Al2O3) were successfully fabricated using powder metallurgy techniques followed by extrusions. The MMCs were selected using various weight fractions alumina powders (Al2O3) as reinforcement particles and matrix of aluminum powders.(1) The Al alloy powder was mixed with 37µm Al2O3 powder in weight fractions of 0, 5, 10, and 15%.(2) The mixed powders were hot pressed under a pressure of 420 MPa and sintered at 450 ?C for 6 hours.(3) Extrusion process was used as secondary manufacturing process to consolidate (Al / Al2O3) composites obtained by pressing mixed powders.(4) Extrusion dies of various extrusion ratios (rx); 4.4, 5.5, 7.1 and 9.5 were used to extrude the MMC at temperature 550 ?C.Physical Properties(1) The MMC densities at various locations were found to increase as weight fractions of particulate reinforcement were increased.(2) The density was also found to increase as the extrusion ratios were increased.(3) The porosity was found to increase as weight fractions of particulate reinforcement were increased. However increasing extrusion ratio resulted in significant decrease in porosity from 2.09 to 0.5 vol.%.(4) The properties of the MMCs depend not only on weight fraction of reinforcement but also on extrusion ratios. The higher extrusion ratio the lower is the porosity.Mechanical properties(1) The composite hardness has been greatly improved by increasing weight fraction of reinforced particles.(2) The yield and ultimate tensile strengths of the MMCs have been increased with increasing the weight fraction of reinforcement particles.(3) A critical weight fraction of reinforced particles, 5 % must be attained before improving the tensile strength.(4) Both tensile strength and hardness were greatly improved by increasing the extrusion ratios.Microstructure(1) The higher extrusion ratios have also showed relatively more homogenous particle distribution with preferred particle orientation to extrusion axis.(2) These results showed that increasing extrusion ratios could be used to produce uniform reinforcement particles distribution in MMCs.(3) Fractographic structure showed bimodal distribution of dimples; the larger dimples are associated with reinforcement particle and smaller dimples are associated with the ductile failure of the matrix.(4) Some reinforcement particles were pulled out of and other showed initiation of cracks across the particles.(5) As extrusion ratio is increased the dimple sizes of reinforcement particles were decreased and the distribution of dimples became more uniform.Machining characteristicsIn machining tests to MMCs, using Carbide inserts as cutting tools with and without coating, the following results were obtained during simple lathe turning tests:(1) Tool life decreased with increasing the cutting speed in all cutting conditions.(2) Coated cutting tools have significantly improved the tool life. Coated tools can increase the tool life with more than 3.3 times of uncoated tools, at cutting speed of 80 m/min.(3) The surface finish of machined surfaces deteriorated when coated carbide tools were used.(4) Wear rate of cutting tool has decreased by decreasing weight fraction of reinforcement particle and/or decreasing extrusion ratio from 9.5 to 4.4. However the effect of weight fraction is more pronounced than effect of extrusion ratio.5.2 Future Work1. Further investigation is suggested to optimize he strength of composites by varying alumina particle size, compacting pressure and temperature.2. It was found that critical weight fraction of alumina particles must be reached before any improvement in mechanical properties. Experimental and theoretical studies are required to determine the effect of processing parameters and reinforcement types on the critical weight fraction.3. It is also suggested further studies on effect of other extrusion parameters such as die angle, lubrication and extrusion speeds on mechanical characteristics of metal matrix composites4. Further investigation is suggested to optimize the effect of other machining parameters such as depth of cut and feed on machining characteristics of metal matrix composites.5. Further investigations are required to understand the surface roughness deterioration and its relation to coatings of cutting tools.6. It is also suggested to study the cohesion, de-cohesion and fracture of the reinforcement particles as result of machining and their relation to surface finish and cutting tool wear.