Microstructure Evolution and Mechanical Property of the Retractable Pin Tool Friction Stir Welding (RPT-FSW) Joints of A356 Aluminum Alloy Wheels

Reducing weight is one of the most important challenges in the automotive industry. A wheel design which enables to reduce weight from 13.5 kg to 10 kg is presented. This achievement is possible thanks to the use of a wide variety of technical processes. The disc is manufactured by CobapressTM, a casting/forging process which combines the advantages of a high design freedom, good mechanical properties and the absence of porosities. The alloy used is an A356 aluminum alloy modified with strontium. The rim is made of an AA6082 aluminum alloy which is extruded and flow-formed with a thickness from 3.3 down to 2.2 mm. Finally, the FSW (Friction Stir Welding) allows us to weld the two parts with a cavity to minimize the weight. With this technique the welding of the two different alloys is possible with good mechanical properties, the fracture happens outside of the weld during tensile tests. The final wheels passed bending and radial fatigue tests as well as radial impact tests with success.

Download Full-text

Submerged Dissimilar Friction Stir Welding of AA6061 and AA7075 Aluminum Alloys: Microstructure Characterization and Mechanical Property

Metals ◽

10.3390/met11101592 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1592

Author(s):

Akbar Heidarzadeh ◽

Mousa Javidani ◽

Mohammadreza Mofarrehi ◽

Amir Farzaneh ◽

X.-Grant Chen

Keyword(s):

Mechanical Property ◽

Aluminum Alloy ◽

Friction Stir Welding ◽

Cross Section ◽

Electron Backscattered Diffraction ◽

Friction Stir ◽

Base Materials ◽

Dissimilar Friction Stir Welding ◽

Mechanical Strengths ◽

Hardness Values

The possibility of underwater dissimilar friction stir welding of AA6061 and AA7075 aluminum alloy was explored to overcome the problem of hardness loss in different microstructural zones. Optical microscopy and electron backscattered diffraction were employed to characterize the microstructure of the joint. Vickers hardness measurements were conducted on the cross-section of the joint to evaluate the mechanical strengths. The results showed that the microstructure of the AA7075 side had undergone the same mechanisms as those occurring during conventional friction stir welding. In the case of the AA6061 side, in addition to typical restoration mechanisms, the grain subdivision was observed. The AA7075 side had finer grains compared to the AA6061 side, which may be related to the different morphology and size of precipitates. Moreover, friction stir welding caused a reduction in the hardness values in all the microstructural areas compared to those of corresponding base materials. For example, it caused a reduction in the hardness of a thermomechanically affected zone from 105 HV to 93 HV in the AA6061 side, and from 187 HV to 172 HV in the AA7075 side. The underwater media improved the overall hardness values in thermo-mechanically affected zones (13% reduction in hardness) compared to those reported in literature (57% reduction in hardness).

Download Full-text