Microstructure and mechanical properties of longitudinal weld in 6005A aluminum alloy profile extruded by a porthole die

Abstract

Porthole die extrusion experiments were carried out on 6005A aluminum alloy under the billet heating temperatures of 420–570 °C and ram speeds of 1–120 mm/min. The effects of extrusion parameters on the microstructure and mechanical properties in the longitudinal weld of profiles were investigated. It was found that the crystal orientation of longitudinal weld region showed the characteristics of gradient arrangement with different oriented grains wrapped in layers and symmetric along the welding line. The Copper{112} grains are formed at the welding line under the combined effect of shear and compression, and the Goss{110} grains are formed on their both sides due to dynamic recrystallization. A shear band is formed when part of metals flow through the 45° inclination angle of port bridge due to a sudden change in velocity, causing the Goss{110} texture in local region to rotate to Brass{110} texture. The 6005A aluminum alloy profiles mainly contain β (Mg2Si) phase, Q (Al3Mg9Si7Cu2) phase, AlCrMnSi phase and AlFeMnCrSi phase. Appropriately increasing billet heating temperature and ram speed can promote dynamic recrystallization and the dissolution of β-phase and Q-phase, thus improving the strength and hardness of the profile. However, when the billet heating temperature is too high, the strength and hardness are reduced instead due to grain coarsening. The profile extruded at billet heating temperature of 510 °C and ram speed of 120 mm/min has the best mechanical properties, with the tensile strength in 0° direction and hardness at the welding line of 179.93 MPa and 52.2 HV, respectively.

Keywords

• Porthole die extrusion
• Grain orientation
• Dynamic recrystallization
• Layer-by-layer shear
• Microstructure
• Mechanical properties