Microstructural and mechanical properties of ZA10 alloy tubes and their weld seams prepared by Conform continuous extrusion

In the present work, Zn–10Al–2Cu–0.05Ti (ZA10) alloy tubes with a diameter of 12.5 mm and wall thickness of 1.2 mm were fabricated by one-pass and double-pass Conform continuous extrusion. A stabilizing heat treatment [350 °C, 30 min (furnace cooling) + 120 °C, 12 h (air cooling)] was also applied to some of the double-pass tubes to improve the quality of their weld seams. The yield strength, ultimate tensile strength, elongation and expansion ratio of the one-pass continuous extrusion tube were 268.4 MPa, 294.3 MPa, 13.8% and 5.5%, respectively. Double-pass continuous extrusion improved these values to 278.4 MPa, 317.2 MPa, 15.4% and 11.4%, respectively. Double-pass tubes also had fewer aggregations of Al-α precipitates along the welding seam, which improved seam quality and caused cracks to appear in the matrix, away from the weld-affected zone, during expansion testing. Heat-treated double-pass tubes exhibited superior yield strength (283.9 MPa) and ultimate tensile strength (328.5 MPa) but lower elongation (10.2%) and expansion ratios (10.3%). Additionally, the heat-treated tubes exhibited markedly lower elongation at room temperature due to the remarkable blockage of dislocation motions by fine-scale lamellar (α + η) eutectoid structures and a lower size effect when stretched.