The Influence of Indirect Hot Extrusion and Heat Treatment Parameters on the Properties of Flat Profiles Made of the Aluminium Alloy EN AW-7475Wednesday (08.11.2017) 15:00 - 15:20 Part of:
The use of in-line cooling after hot extrusion provides an apparent advantage in terms of energy saving, shorter production time and cost savings compared with separate annealing in a vertical furnace and subsequent bath quenching. Furthermore, spray cooling on the output table upon availability of the puller aids in decreasing the profile’s distortion. However, the possibility of an in-line heat treatment may be limited if critical quenching times have to be observed. This is evident especially in the case of hard deformable alloys of the type EN AW-7xxx because the critical time is short and the extrusion speed is comparably low in order to prevent hot cracks as well as high extrusion forces. In the present work, the process of integrated quenching after indirect extrusion is considered for the manufacturing of flat profiles made of alloy EN AW-7475 with dimensions of 8.7 x 87 mm and 6.8 x 86 mm on a 15 MN extrusion press. Extrusion ratios equalled 28:1 and 37:1, respectively. Extrusion speed was varied from 1.7 to 3.2 m/min. A tunnel-like water-cooling device was employed to ensure the in-line cooling. Subsequent heat treatments were carried out both for T5 (with in-line cooling) and T6 condition (with separate quenching following solution annealing at 477 °C). The following types of one-step artificial ageing were used: 120 °C for 24 h; 160 °C for 4 or 8 h. The influence of the extrusion parameters on the output temperature of the profiles, their electrical conductivity and mechanical properties were investigated. A significant correlation between the electrical conductivity and the yield strength in the T5 and T6 conditions was obtained. The experiments revealed that in-line quenching during extrusion with a profile speed of 3.2 m/min followed by artificial ageing at 120 °C for 24 hours provided yield strengths of more than 500 MPa.
|Category||Short file description||File description||File Size|
|Short Paper||366 KB||Download|