Properties in Tension of Semi Continuous Cast and Extruded Zn-22Al-2Cu alloy

Abstract

Circular bars of the Zn-22Al-2Cu alloy were prepared by utilizing the semi continuous vertical casting technique. Solid as cast showed high values in the mechanical strength (497 MPa) and hardness (71 R B ). The micro structure of the bars consisted of equiaxed dendrites with eutectoidal composition surrounded by eutectic. At higher magnifications it can be observed that dendrites are two-phase eutectoid cells with lamellar structure. X-ray diffraction studies revealed that phases α' S , η' S and ε are present in such circular bars with ε phase as second phase particle. Later, the bars were preheated at 523 K then extruded, observing that, with preheating, the hardness value diminish down to 33 RB. By analyzing a piece of bar, it was observed that with preheating the ε phase disappears and there is a coarsening of lamellas at interior of cells and interdendritic space. Finally, the results of the tension tests showed that elastic modulus and tensile strength values, decrease substantially after extrusion, while the ductility value is increased.