The objective of this work is the comparison of the properties of aluminium alloys produced by two different routes. The alloys are Al-Fe base or Al-Fe-X plus ceramics types designed for high strength at low to medium temperatures. The first route, mechanical alloying, has been optimized on prealloyed Al3Fe powders. Evaluation of the mechanical properties has indicated a 5O% increase in the strength at temperatures up to 400C. In the second part of the project, elemental powders of Al, Fe and Mn have been mechanically alloyed in a weight composition Al- (5)Fe-(4)Mn. The aim is to further increase the properties with at least the same stability at elevated temperatures.
Research carried out compared the aluminium iron alloys designed for elevated temperature use and processed by different routes. The 2 processing routes studied were mechanical alloying and in situ microfusion (ISM).
The process of mechanical alloying has been optimised for prealloyed Al-3wt% Fe powders and for a blend of elemental powders having a mean composition Al-5wt%Fe-4wt%Mn. Both mechanically alloyed powders have been hot consolidated by extrusion or forging. Tensile strength of 570 MPa at room temperature and 350 MPa at 300 C have been reached. After annealing for up to 100 h, the elevated temperature properties are conserved. In the in situ microfusion process, a liquid phase is generated by the intense exothermic reaction between aluminium and elemental iron during a sintering cycle, leading to a dispersion of Al3Fe intermetallics. A strength level of 175 MPa and a ductility of 19% have been achieved with a Al-13wt% Fe using a prealloyed Al-3wt% Fe powder as matrix. In order to increase the properties, the as sintered products need to be consolidated, which results in an increase of the tensile strength by 50 MPa. ISM techniques produced alloys with weak mechanical properties.
Research was carried out to develop new light aluminium alloys for application at elevated temperatures (300-350 C) in the automotive industry. Classical wrought, and precipitation hardened, aluminium based alloys lose their strength at about 150 C and do not fulfil requirements.
A process of double mechanical alloying has been developed with a reaction stage using elementary or prealloyed powders by which aluminium alloys could be used at elevated temperatures in the automotive sector. Ductility, however, has to be improved. This route, preferable to the alternative of in situ microfusion, is expensive and can be used only when there is no alternative. Neither the effectiveness nor the cost implicit in the objective were maximised or minimised. The project was completed within schedule but more costly and riskier research would have to be carried out if a satisfactory alloy is to be obtained.
THE ALLOYS OF AL-FE, AL-FE-X, OR AL-FE-X PLUS CERAMICS TYPES ARE DESIGNED FOR HIGH STRENGTH AT LOW TO MEDIUM TEMPERATURES (UP TO 300 CELSIUS DEGREES).
INDEED THE IMPORTANT HARDENING DUE TO THE PRESENCE OF FINE DISPERSIONS OF INCOHERENT PHASES FORMED DURING THE SOLIDIFICATION OR DURING THE POWDER METALLURGICAL PROCESSING, ASSURES THE THERMAL STABILITY OF THE STRUCTURE. THE MORE CLASSICAL ALLOYS ARE AL-FE WITH ADDITION ELEMENTS LIKE CE, ZR, MO.
PROCESSES TO BE ASSESSED ARE RAPID SOLIDIFICATION TECHNOLOGY (RST), MECHANICAL ALLOYING (MA), AND NEL'S "IN SITU MICROFUSION" PROCESS (ISM)
ASSESSMENT OF THE PROPERTIES AND STRUCTURES AVAILABLE FROM THESE ROUTES WILL ENABLE PROCESSES TO BE DEVISED UTILISING THE BEST FEATURE OF SOME OR ALL OF THE TECHNIQUES.
THE POTENTIAL APPLICATIONS OF POWDER METALLURGY ALUMINIUM ALLOYS WOULD BE IN THE AUTOMOTIVE INDUSTRY.
THIS STUDY WILL ALLOW THE DIRECT COMPARISON OF THE TWO PROCESSES BY PRODUCTION OF THE SAME ALLOY COMPOSITION. FURTHER DEVELOPMENT IS PLANNED TO IMPROVE MATRIX STRENGTH BY MEANS OF USING RAPIDLY SOLIDIFIED ELEMENTARY POWDER AND BY CERAMIC REINFORCEMENT. EACH PROCESS WILL BE EVALUATED FROM A TECHNICAL- ECONOMICAL POINT OF VIEW. IT WILL LEAD TO A BETTER COMPROMISE BETWEEN THE MATERIAL CHARACTERISTICS AND THE FORMING BEHAVIOUR RELATED TO AUTOMOTIVE APPLICATIONS.
Funding SchemeCSC - Cost-sharing contracts
G75 0QU Glasgow