Investigation into the Effect of RFSSW Parameters on Tensile Shear Fracture Load of 7075-T6 Alclad Aluminium Alloy Joints.

Andrzej Kubit,Ján Slota,Tomasz Trzepieciński,Wojciech Bochnowski,Elżbieta Gadalińska

doi:10.3390/ma14123397

Abstract

The aim of the investigations was to determine the effect of parameters of refill friction stir spot welding (RFSSW) on the fracture load and failure mechanisms of the resulting joint. RFSSW joints were made in 7075-T6 Alclad aluminium alloy sheets using different welding parameters. The load capacity of joints was determined under tensile/shear loadings. Finite element-based numerical simulations of the joint-loading process were carried out, taking into account the variability of elasto-plastic properties of weld material through the joint cross-section. The influence of welding parameters on selected phenomena occurring during the destruction of the joint is presented. The considerations were supported by a fractographic analysis based on SEM images of fractures. It was found that there is a certain optimal amount of heat generated, which is necessary to produce the correct joint in terms of its load capacity. This value should not be exceeded, because it leads to weakening of the base material and thus to a reduction in the strength of the joint. Samples subjected to uniaxial tensile shear load showed three types of failure mode (tensile fracture, shear fracture, plug type fracture) depending on the tool rotational speed and duration of welding. Prediction of the fracture mode using FE-based numerical modelling was consistent with the experimental results. The samples that were damaged due to the tensile fracture of the lower sheet revealed a load capacity (LC) of 5.76 KN. The average value of LC for the shear fracture failure mechanism was 5.24 kN. The average value of the LC for plug-type fracture mode was 5.02 kN. It was found that there is an optimal amount of heat generated, which is necessary to produce the correct joint in terms of its LC. Excessive overheating of the joint leads to a weakening of the base metal and thus a reduction in the strength of the joint. Measurements of residual stresses along the axis specimens showed the presence of stresses with a certain constant value for the welded area on the side of the 1.6 mm thick plate.

Highlights

IntroductionThe growing demand for light and easy-to-recycle alloys from the automotive and aerospace industries opens a window for a new use of aluminium alloys [1,2]
Licensee MDPI, Basel, Switzerland.The growing demand for light and easy-to-recycle alloys from the automotive and aerospace industries opens a window for a new use of aluminium alloys [1,2]
Alclad 7075-T6 aluminium alloy sheets with thicknesses of 1.6 mm and 0.8 mm were used as the test material for the fabrication of single-lap refill friction stir spot welding (RFSSW) joints

Summary

Introduction

The growing demand for light and easy-to-recycle alloys from the automotive and aerospace industries opens a window for a new use of aluminium alloys [1,2]. These alloys create difficulties when joined with conventional welding techniques because they create brittle intermetallic compounds in the microstructure that cause intermetallic cracks [3]. Solid state welding makes it possible to eliminate this drawback. High strength aluminium alloys, i.e., AA7075, can be safely arc welded without hot cracks by introducing nanoparticle-enabled phase control during welding [5]

Methods

Results

Conclusion