Formation of Globular Structures in Aluminum A356 Alloy by Narrowmelt Stream (NMS) Technique

Narrow Melt Stream (NMS) is a relatively new semisolid metal processing technique for producing globular structures in alloys. This method is based on pouring the melt through a small sized nozzle into a mould located at a certain height under the crucible. This simple method generates globular structures without using equipments such as impellers, electromagnetic stirrers, ultrasonic probes and cooling slopes. Therefore it is cost effective. In the present study, the effect ofcasting size and mould casting modulus on the globular structure evolution in A356 aluminium alloy specimens prepared by NMS process was investigated. The results showed that regardless of the different casting modulus and their sizes, all the specimens exhibited globular structures. However, the size and shape factor of the globules decreased with increased casting modulus and casting size indicating the influential effect of the surface area of the mould in generating globular structures in this process.