Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Powder pretreatment
Patent
1993-09-21
1994-09-06
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Powder pretreatment
419 38, 419 44, 419 54, 148513, 148514, B22F 100, B22F 316
Patent
active
053446054
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of degassing and solidifying a rapidly solidified aluminum alloy powder.
BACKGROUND TECHNIQUE
As a method of forming and solidifying a rapidly solidified aluminum alloy powder, there are various methods, for example, extrusion method, HIP method, powder forging method, etc. For solidifying a powder, it is necessary to heat the powder by all means, during which the quenching effect of the powder is lost to deteriorate the properties. Prevention of this deterioration is carried out by rapidly heating in a short time. A patented invention relating to carrying out rapidly heating for the purpose of solidifying a rapidly solidified aluminum alloy powder is 1. U.S. Pat. No. 4,435,213: "Method for Producing Aluminum Powder Alloy Products Having Improved Strength Properties; Alcore", a patented invention relating to induction heating of general powders, not limited to aluminum, is 2. U.S. Pat. No. 5,134,260: "Method and Apparatus for Inductively Heating Powders or Powder Compacts for Consolidation; Carnegie Melon University" and a patented invention relating to rapidly heating by hot air is 3. Japanese Patent Laid-Open Publication No. 158401/1991: "Method of Heating Rapidly Solidified Powders; Kubota".
To any one of the above described powder forging method, extrusion method and HIP method, well known in the art, is indispensable the heating before solidification because of 1. decreasing a deformation resistance of a powder and shaping the powder with a low stress and 2. degassing.
In particular, the degassing is an indispensable means for preventing a solidified article from forming of bubbles called blistering and in the case of the powder forging, strongly bonding grains with each other, for example, like known methods described in Japanese Patent Laid-Open Publication No. 224602/1987 and "Kei-Kinzoku (Light Metals)" 37 (10) 1987, page 656-664.
In the prior art techniques, degassing has generally been carried out by can-sealing a CIP (cold isotactic pressing) body and heating in vacuum or in an inert gas atmosphere at a temperature of 400.degree. to 600 .degree. C. Any prior art method has aimed at completing sufficiently degassing by raising the temperature for 0.5 to 2 hours and maintianing a predetermined temperature for 0.5 to 2 hours, amounting to 1 to 4 hours, using an ordinary resistance heating furnace.
However, it has hitherto been pointed out that the above described degassing method has the disadvantages that the quenching effect of a powder, i.e. the effect of precipitating finely and unifromly an element or phase which tends to be coarsely precipitated at an ordinary cooling rate or the effect of rendering crystal grains fine is lost by heating for a long time to deteriorate the properties of a shaped and solidified body, and moreover, prevention of oxidation during then needs controlling of the atmosphere, resulting in rising of the production cost.
Heating rapidly and uniformly a material having a low heat conductivity such as green compacts has generally been considered difficult. Ordinarily, the most suitable method for rapid heating on a commercial scale is an inductive heating. For example, it has been reported in Japanese Laid-Open Publication No. 134503/1974 that for powder metallurgy of a ferruginous metal, a high frequency induction heating is utilized for heating and sintering a green compact. Up to the present time, such a high frequency inductive heating has been utilized for previous heating in sintering in a shorttime or sintering forging (forging for increasing the density of a preform which is being sintered).
However, the inductive heating has not been used for degassing of a green compact of aluminum powder or aluminum alloy powder. The reasons therefor are as follows:
It has been considered that the presence of a stable alumina film (Al.sub.2 O.sub.3) with a low electric conductivity on surfaces of aluminum powder or aluminum alloy powder results in increase of the resistance of the powder and decrease of the electric conduc
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Akechi Kiyoaki
Kaji Toshihiko
Odani Yuusuke
Takeda Yoshinobu
Tanji Takao
Jenkins Daniel J.
Sumitomo Electric Industries Ltd.
Walsh Donald P.
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