FSW-Leg – Synthesis of non-equilibrium alloys using friction stir welding processes

Motivation

Friction Stir Processing (FSP) is a process that closely resembles Friction Stir Welding (FSW). From a materials science perspective, the processing of materials using friction processes such as FSP and FSW is very interesting because of the one-of-a-kind conditions that the material experiences during processing. The resulting properties of the seam are especially prized because of the refined processing zone, which displays a fine microstructure resulting from dynamic recrystallization.

Various publications address the mechanical alloying of materials using friction stir processes. The research presented almost always include material characterization; however, the results are rarely tied back to the process parameters. Because of this, there is a lack of comprehensive knowledge about the alloying process (e.g. what the most important factors are). This also means that the process parameters cannot yet be tuned in order to produce a material with the desired properties.

Project Goal

The goal of this project is to deepen process understanding in the field of mechanical alloying using friction stir processing. This requires an analysis of both the significant process parameters as well as the metallographical development during the alloying process.

Procedure

First, a suitable process apparatus and the appropriate material characterization methods must be determined. One branch of experiments will be based on sheets of a 2xxx-series aluminum, into which zirconium will be processed. Zirconium has been shown to hinder recrystallization and grain growth during heat treatment. In a second branch of experiments, an AA1050 aluminum will be processed to include iron (Fe), which has a low solubility in aluminum, as well as copper (Cu), which has a relatively high solubility in aluminum and has a higher deformability than iron. Special attention will be given to the design of the experiments in order to save materials and generate meaningful results without extraneous experiments. Additionally, the experimental set-up will be developed in order to allow for a simple and robust monitoring of process values (i.e. temperature, torque, process forces, etc.). Material characterization will be performed using methods such as optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM).

The mechanical alloying process using FSP will be analyzed based on the experimental results. Here, special attention will be payed to the process energy input as well as the distribution of the secondary elements in the processing zone. For this, statistical tools from Design of Experiments (DoE) will be used, and chosen parameters, such as the morphology of the secondary element and the method of integration will be systematically varied. From these results, a strategy for effective alloying using FSP will be formulated. Additionally, an empirical model will be generated to tie the process input parameters to the resulting material properties.  

Acknowledgment

„FSW-Leg“ is funded by the Deutsche Forschungsgemeinschaft (DFG).