INFLUENCE OF THE STRUCTURE AND TEMPERATURE ON THE EXTRUSION PRESSURE OF AN ZN-20AL-2CU ALLOY

The feasibility of developing a method to successfully extrude the eutectoid Zn-Al alloy modified with 2 mass% Cu was studied. The best conditions found for extrusion are determined by the dendrite size of the extrusion ingot, the extrusion rate, and the extrusion temperature. Alloys extruded below the eutectoid temperature show high strength (380 MPa) and good ductility (25-35%). The microstructure of this alloy is composed of fine grains of aluminum solid solution a and zinc solid solution eta and epsilon phases. When the alloy is extruded between 280 degrees C and 320 degrees C, the resultant alloy is super plastic with microstructure formed by fine grains (0.5 mu m to 2 mu m). Higher extrusion temperatures, cause embrittlement of the material, likely caused by the presence of a low melting point Zn rich eutectic phase at the grain boundaries formed during the solidification.