Influence of Post-Weld Heat Treatments on Microstructure and Mechanical Properties of Laser Beam Welded 2060-T3/2099-T3Al-Li T-Joints

Yunlong Zhang,Tiantian Nan,Wang Tao,Zhaohui Yang,Zhenglong Lei,Yanbin Chen

doi:10.3390/met9121318

Abstract

The durable structure and robustness of T-joints in the panel materials for civil aircraft are a crucial matter of importance. In this work, the impact of the post-weld heat treatments (PWHTs) on the microstructure and mechanical properties of laser beam welded T-joints of 2060-T3/2099-T3 Al-Li alloy was analyzed. Heat-treatment of the laser beam welded T-joints was carried out in two different ways, namely, solution treatment and artificial aging (STAA) at varied duration and only artificial aging (AA) at varied duration. The microstructure and mechanical properties of the heat-treated joints were investigated using metallographic and scanning electron microscopic images, micro-hardness test, and tensile test, respectively. The results showed that, in cases of STAA, the eutectic structures on the grain boundary were partially dissolved via solution treatment (ST), and increased dispersed precipitation of the second phase in matrix resulted in significant dispersion strengthening, as well as enhanced strength and plasticity. In contrast, in the AA process, alloy elements in the matrix continued to segregate towards the grain boundary, resulting in significant grain boundary strengthening, enhanced strength, and decreased plasticity. Additionally, joint fractures were micro-porous aggregation transgranular ones in the fusion zone (FZ). The joints treated by STAA exhibited excellent plasticity compared with those treated by AA. Furthermore, the micro-hardness of welded joints treated by AA was higher than that of those treated by STAA. Indeed, the tensile strength of joints treated by STAA and AA ranged from 405 to 475 MPa, which was 81–95% of the base metal 2060-T8, though the elongation of joints treated by STAA was superior to the counterpart AA.

Highlights

Compared with traditional aluminum alloy, Al-Cu-Li alloy is highly promising for applications in the aerospace industry owing to its low density, high elasticity module, high specific stiffness, and high specific strength [1,2,3,4], and 2060/2099 Al-Li alloys are one of the alloys in the Al-Cu-Li alloy system.For each 1% Li added, the density of the aluminum alloy is reduced by 3% and the elastic modulus is increased by 6% [1,2]
The tensile fracture, micro-hardness, and microstructure of the welded T-joints heat-treated by solution treatment and artificial aging (STAA) (165 °C for 20 h) and artificial aging (AA) (165 °C for 20 h) were recorded for a comparable analysis of the joint strengthening effects, which was caused by the heat treatment of STAA and AA, distinctively
Laser beam welded 2060-T3/2099-T3 Al-Li alloy based T-joints were heat-treated by STAA and AA after welding at various process parameters

Summary

Introduction

Compared with traditional aluminum alloy, Al-Cu-Li alloy is highly promising for applications in the aerospace industry owing to its low density, high elasticity module, high specific stiffness, and high specific strength [1,2,3,4], and 2060/2099 Al-Li alloys are one of the alloys in the Al-Cu-Li alloy system. For each 1% Li added, the density of the aluminum alloy is reduced by 3% and the elastic modulus is increased by 6% [1,2]. Al-Li alloys, especially those consisting of volatile metal elements such as. Li and Mg, are readily exposed to solidification cracking and pore defects during fusion welding, resulting in poor weld formation [5,6,7,8]. Ramulu et al [9] employed tungsten inert gas arc to weld

Methods

Results

Conclusion