Semisolid Joining of Zinc AG40A Alloy by Partial Remelting and Mechanical Stirring

摘要

A technique to achieve the globular weld structure using stirring the localized semisolid zone during butt-joining of zinc AG40A (Zamak-3) die cast alloy is reported. Since the semisolid temperature range of this alloy is very narrow, the accurate controlling of weld pool temperature must be considered. By presented process, globular microstructure of the weld zone can be achieved. Moreover the near weld zone would have the globular structure due to semisolid holding. A gas heating system was designed to heat up the nitrogen gas to desired temperature accurately. A heating element was embedded in a castable ceramic block while a stream of gas could pass closely around the hot element length. Hot nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool. At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Local mechanical properties of different zones show a good strength in the weld metal zone and heat affected zone by results of the shear punch tests and hardness tests. Air entrapment in the pool decreases by controlling the speed of substrate movement and stirrer rotation under the nozzle. The strengths of each zone show relative correspondence to the variation of the hardness values.