Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Consolidation of powder prior to sintering
Patent
1995-11-30
1997-03-18
Jordan, Charles T.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Consolidation of powder prior to sintering
419 46, 75249, B22F 316, C22C 104, C22C 2102, C22C 2104
Patent
active
056131844
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to aluminium alloys and to a method for their production by a powder metallurgy route.
With the ever increasing emphasis on improved fuel economy and reduced emission levels for internal combustion engines in vehicles, there is a consequent trend towards making vehicles and the components which go into them lighter in weight. Examples of this trend include the increasing use of aluminium cylinder heads in engines and various components in aluminium alloy which at one rime were made in cast iron, for example.
In general, aluminium alloys are considered to be good candidates for replacing some automotive components due to their relatively high strength to weight ratio. Additionally, their good corrosion resistance and high thermal conductivity make such alloys attractive for some applications within a vehicle.
Increasingly, silicon-containing aluminium alloys are now being considered for wear-resistant applications in the engine in addition to structural applications on the vehicle. Examples of such applications where wear-resistance is needed are in camshaft pulleys, rotors for air-conditioning units, pistons and tappets. Generally, aluminium alloys in vehicle applications have been produced by casting and machining or forging and machining. It is highly desirable to be able to produce a component to near net-shape and to minimise the amount of subsequent machining required.
Aluminium silicon alloy materials made by a powder metallurgy route have generally been fully or nearly fully densified by subsequent forging or extrusion operations or the like to give a strong, relatively uniform structured material from which a part is then machined. Sintering of fully pre-alloyed aluminium/silicon powders without additional sintering aids, has been seen as a difficult and unreliable process, particularly for hypereutectic aluminium/silicon compositions. The tenacious oxide film on aluminium powder particles inhibits bonding of the powder particles during sintering.
It is an object of the present invention to produce an aluminium silicon alloy having an overall hypereutectic composition and provide a method for its production which will allow alloys suitable for some wear-resistant and structural applications to be produced by a near net-shape compaction-and sinter powder metallurgy route. It is a consequence of the present invention that, because of the high silicon content, the compaction process is eased compared with conventional aluminium powder metallurgy materials, and galling (sticking) of the compaction die is much reduced. According to one aspect of the present invention there is provided a method for the production of an aluminium alloy by a powder metallurgy route, the method comprising the steps of producing at least a first powder of a near-eutectic aluminium-silicon based alloy; producing at least a second powder of a hypereutectic aluminium-silicon based alloy; mixing desired proportions of the at least first and second powders together; compacting the powder mixture and sintering the compacted powder.
Hereinafter, the term "near-eutectic" aluminium-silicon based alloy refers to an aluminium alloy containing from 9 to 13 wt % of silicon. The position of the eutectic point is influenced by additional alloying elements and by the solidification parameters experienced by the powder during manufacture. Similarly, for the purposes of this specification, a hypereutectic aluminium-silicon based alloy is defined as comprising more than 13 wt % of silicon.
One or both of the constituent first and second aluminium alloy powders may contain further alloying additions which confer improved properties by, for example, solution hardening and/or precipitation hardening.
One or both constituent first and second aluminium alloy powders may have compositions which, at the interparticulate interfaces generate a transient liquid phase to further assist the sintering operation.
The alloy powders may be made by one or more of the currently known powder production methods.
The powder mixture ma
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Mahmoud Mohammad S.
Purnell Charles G.
Smith Paul
Brico Engineering Limited
Jenkins Daniel
Jordan Charles T.
The Aluminium Powder Company Limited
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