Intermediate annealing treatment as an effective tool for suppression of abnormal grain growth at longitudinal weld of 2196 Al–Cu–Li profile

Abstract

The longitudinal weld of extrusion profiles will form dramatic abnormal grain growth (AGG) during solution treatment, leading to performance deterioration. A modified heat treatment method, i.e., an intermediate annealing treatment (IAT) was inserted into standard T6 treatment was proposed in this paper to alleviate AGG of longitudinal weld. 2196 Al–Cu–Li profiles with longitudinal weld were subjected to IAT with different parameters, and the grain growth behavior and microstructure evolution of them were studied. The processing window of IAT was determined as 450 °C/0–60 h and 475 °C/0–6 h and some parameters in between, the reasonable IAT temperature is below solution treatment about 50 °C. IAT at 450 °C/24 h is the most noticeable parameter for the suppression of AGG, a narrow AGG area formed during this IAT, and the fine grains surrounded AGG area exhibited continuous uniform coarsening, leading to releasing of sub-grain boundary energy and decreasing of driving force for AGG by 50%. Besides, many secondary phases formed during IAT and work as pinning particles, hence the width of AGG area in this sample reduced 90% compared to that of T6 samples, and the tensile strength increased about 20 MPa and the elongation increased by 42%.