With rapid solidification supersaturated Al-Si- X-Y alloys can be envisaged which possess a good combination of strength, especially at high temperature (up to 350C), wear resistance and a moderate coefficient of thermal expansion. The feasibility of four processing routes is investigated, two of them based on gas atomized powders and two on spray deposited preforms. Two routes rely on extrusion and the other two on sinter-forging for the final densification. Spray deposition routes are likely to be cheaper than gas atomization processing and likewise forging is presumably cheaper than extrusion. Although only one composition is considered which is fairly well documented (at least for one of the processing routes considered) a long list of manufacturing parameters was investigated: granulometry of the powder, extrusion and forging temperatures, extrusion ratios, effect of ageing, etc. The project ends with the fabrication and the expertise of pistons.
Investigations were carried out to produce low cost and efficient pistons for automobile manufacturing and to maximise the effectiveness cost relationship of the aluminium silicon iron nickel alloy, Al-20Si-5Fe-2Ni (wt%). The end result is a new aluminium alloy obtained by producing supersaturated aluminium silicon (Al-Si-X-Y) alloys using rapid solidification.
The attention has been focussed on optimisation of the hot forming parameters and on the mechanical behaviour. The rheological studies showed that beyond a critical hot deformation, the microstructure and the constitutive rheological laws of all materials (produced from powders or from preforms) are quite similar.
Parameter optimisation included the effect of the extrusion ratio, of the forging ratios, of the powder particle size distribution. The effect of ageing was investigated throughmicrostructural studies coupled to differential scanning colorimetry (DSC) which show an evolution in the precipitates. Generally the effect of ageing is not detrimental to the mechanical behaviour and may be positive for materials with a fine microstructure. The elevated temperature properties of most materials are quite attractive and good compromises between the level of properties and processing costs are in sight. Forging of components has been undertaken and preliminary results are encouraging. Work is programmed beyond the programme duration to expand some investigations.
AL-SI ALLOYS (CLOSE TO THE EUTECTIC) ARE WIDELY USED IN THE AUTOMOTIVE INDUSTRY, ONE OF THE REASONS BEING THEIR GOOD CASTABILITY.
TWO TECHNIQUES HAVE BEEN USED UP TO NOW: RAPID SOLIDIFICATION AND THE POWDER METALLURGY ROUTE.
WITH RAPID SOLIDIFICATION SUPER-SATURATED ALLOY (UP TO 30% SI) CAN BE ENVISAGED. WITH POWDER METALLURGY HIGH TEMPERATURE ALLOYS OF THE AL-2OSI-5FE-2NI- TYPE CAN BE PRODUCED WITH GOOD THERMAL PROPERTIES.
THE SPRAY FORMING, WHICH MUST BE REGARDED AS AN INTERMEDIARY TECHNIQUE, ENABLES THE PRODUCTION OF RATHER LARGE PREFORMS, WHICH DO NOT REQUIRE A HIGH EXTRUSION RATIO.
THE INDUSTRIAL APPLICATIONS FOR THE SPRAY FORMING TECHNIQUES MAY BE ESTIMATED TO BE A FEW THOUSAND TONS A YEAR IN THE EEC ALONE.
Funding SchemeCSC - Cost-sharing contracts