STRUCTURE AND PROPERTIES OF POWDER METALLURGY Al/Al-Si-Fe-Cu-Mg COMPOSITES WITH CHEMICAL COMPOSITION GRADIENT

Gradient materials are a unique type of composite, formed from two distinct constituents, which exhibits a graded composition, appearing to transform from one material to another, thus producing gradual changes in characteristics and resultant new exploitable functional properties. Accordingly they extend the range of solutions for constructional components. Research to extend the development of these materials are directed mainly towards obtaining experimental data necessary for working out their optimum chemical composition, microstructure and properties, and also developing methods of manufacture and processes of forming semi and finished products. Aluminium and aluminium alloys form an important group of gradient materials with potential for manufacture of low density construction parts. Aim of this research was, using Powder Metallurgy and subsequent plastic work and heat treatment, the production of composite with gradient chemical composition from the aluminium and its alloy Al-Si-Fe-Cu-Mg. Gradient composite preforms were manufactured by cold pressing aluminium, RAl-1, and aluminium alloy Al17Si5Fe3Cu1.1Mg0.6Zr, designated Al17, powders. Concentration changed from 0 to 100% alloy at 20% intervals. The performs were closed - die forged at a temperature of 490 degrees C and their structures and mechanical properties after forging and additional heat treatment studied. Materials from RAl-1, aluminium alloy Al17 and some mixtures were without porosity. The influence of chemical composition gradient on material flow and tensile, bend and compression properties was examined. Increase in Al17 content increases the compressive strength, but decreases plasticity: on fractographs the increase in brittle regions is visible. Chemical composition of the specimens influenced stress-strain dependence during compression test. In gradient materials there was a pronounced anisotropy in compressive strength with values perpendicular to the concentration gradient being approximately double compared to parallel to the gradient. Optimum strengths were for Al-80% Al17 material: tensile - 219 MPa and compressive - 620 MPa, respectively. The value of compressive strength for the gradient material, measured perpendicular to the concentration gradient and plasticity are comparable with the Al-60% Al17 material.