Session: 03-06-01: Advanced Material Forming – Mechanism, Characterization, Novel Processes, and Control

Paper Number: 149913

149913 - Translating Local Property Enhancements From Friction Stir Processing of Aluminum 7075 Sheets to Global Formability Improvement: Experiments and Modeling 

In an automotive body, different areas perform different functions, typically requiring different materials. This requirement for multiple materials can be detrimental in a few ways. Having to use more material types increases joining and manufacturing costs. Additionally, while aluminum is ideal for cost-effective recycling, multiple alloys complicate the recycling process and increase costs. Although meeting multiple material property requirements within a single material would be an optimal solution, achieving it is challenging. For instance, an Aluminum alloy that is both strong and formable at room temperature can be hard to find. Aluminum 7075 in T6 condition is extremely strong but lacks formability. In such cases, selectively processing A7075-T6 to enhance formability at targeted locations could be a solution. Friction stir processing (FSP) is one such processing technique. FSP is a solid-phase technique like friction stir welding (FSW). While FSW aims to form joints by stirring and heating the material under the tool, FSP uses the same mechanism to modify microstructure locally. However, while FSW, through stirring and heating the material under the tool, aims to join, FSP aims to modify the microstructure of a specific region.

In this study, we first present the bendability results of Friction Stir Processed (FSP) A7075-T6 under various processing parameters. Assuming bendability from VDA correlates to formability, the results demonstrate that the formability of the processed regions increased in all cases, with yield stress decreasing and ductility increasing. Asymmetry was also observed in the results, with the top/tool shoulder side being less bendable in tension compared to the bottom side. The remainder of the study focuses on developing a modeling approach to enable the forming of large-scale parts by designing optimal processing paths.

For this purpose of simulating component level forming, finite element modeling in Abaqus software was utilized. The model incorporates a ductile fracture model and accounts for material heterogeneity in all FSP regions, such as the stir zone (SZ) and heat-affected zone (HAZ). The first step involved determining heterogeneous material properties, such as yield stress, strain hardening, and ductility, through a combination of hardness tests and calibration with uniaxial and VDA bending tests. During this calibration process, it was revealed that although the HAZ and SZ have similar yield stresses, the HAZ exhibited significantly higher ductility. This finding explained the top-bottom asymmetry observed in the VDA bending tests. The validity of the determined local properties was confirmed by comparing a limiting dome height (LDH) forming test with its simulation. This comparison also explained why the base metal is more formable for a specific processed zone design. This study then demonstrates a pan-forming simulation that showed successful forming only after FSP. Based on all the results of this study, in an effort to establish guidelines on the use of FSP for improving formability, we discuss the kinds of forming operations that can be improved by FSP and corresponding processing regions.

Presenting Author: Kranthi Balusu Pacific northwest national lab

Presenting Author Biography: Kranthi Balusu specializes in computational modeling and mechanics of materials. Kranthi is experienced with a wide variety of multiscale & multiphysics computational modeling methods in solid mechanics. In addition, his work involves the formulation & development of these computational methods. His modeling expertise has been applied to a wide variety of materials such as biological tissues, metals at the scale of dislocations and crystals, and composite materials at a microstructural level.

Kranthi obtained his bachelor’s in aerospace engineering and master’s in applied mechanics from the Indian Institute of Technology Madras (IITMadras). He has earned his Ph.D. in aerospace engineering from the University of Texas at Arlington, with a dissertation in microscale plasticity.

Kranthi has been a postdoc at PNNL since 2021. Here, his modeling work on projects from the DOE’s vehicle technology office (VTO) assists in the efficient development and deployment of advanced manufacturing techniques. He is always interested in opportunities that would allow him to develop and utilize a broader variety of computational methods and apply them to a broader variety of materials, material processes, and behaviors.

Authors:

Kranthi Balusu Pacific northwest national lab
Shivakant Shukla Pacific northwest national lab
Hrishikesh Das Pacific northwest national lab
Ayoub Soulami Pacific northwest national lab
Piyush Upadhyay Pacific northwest national lab