2008 Volume 49 Issue 569 Pages 589-594
Powder metallurgy methods have disadvantages resulting from multistage processing, typically consisting of powder production, sizing, compaction and sintering, and this processing often leads to a high cost and low quality because of oxide contamination. As a new powder metallurgy process, it is considered that near-net-shape preforms can be obtained in one step directly from molten metal by an integrated atomization/deposition operation. In the end of the 1960s, this concept was introduced by the Swansea University and adopted by Osprey Metals Co. in the UK. Consequently, this process came to be known as the Spray Deposition Process, Spray Forming Process or Osprey Process. In this study, a new metallurgy process without using powder has been developed to obtain dense preforms with fine-grained and macrosegregation-free microstructures. This technology requires no multistage processing as mentioned above because of the rapid production of solidified metals in thick film sections in one step directly from melt spinning by the integrated filament/deposition operation. The process has been named the Ejection Forming Process, for which a patent is pending in the case of application to AZ91 magnesium alloy. It is shown that the most suitable ejection temperature ranges from 650 to 710°C, which far exceeds the liquidus and a very fine grain size of 15∼20μm is obtained.
