Material stirring and heat generation in friction stir welding processes induce significant microstructure and material properties alterations. Previous studies highlighted the relationship among microstructure, grain size, microhardness, and performance of the joint. In this context, an opportune definition of process parameters, in particular rotating and welding speed, is crucial to improve joint reliability. In this article, results provided by a numerical and experimental investigation on the influence of rotating and welding speed on microstructure, mechanical properties, and joint quality in AA2024-T3 friction stir welded butt joints are reported. Experimental data are presented and discussed considering numerically computed temperature and strain rate distributions, providing useful information for parameters setting. Processing window, i.e., parameters resulting in a successful material deposition, is also individuated.

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Influence of Process Parameters on Microstructure and Mechanical Properties in AA2024-T3 Friction Stir Welding

Detailed thermal and material flow analyses of friction stir forming using a three-dimensional particle based model

Aluminium silicon carbide (Al-SiC) nano composites find its application in gas turbine exit vane, structural parts of automobile and other structural applications. In the present investigation, optimization of the process parameters on mechanical and wear properties of aluminium SiC nanocomposites fabricated via friction stir processing (FSP) was studied. Three process parameters such as number of passes (A), rotational speed(B) and transverse feed(C) were used. For three factors and three levels, L9 Taguchi method was used to formulate the experimental design. Desirability approach is used to optimize the process parameters in terms of tensile strength, microhardness and wear loss. It is observed that the number of passes is the vital process parameter for tensile strength whereas rotational speed is the vital process parameter for microhardness. For three number of passes, 1500 rpm of rotational speed and 70 mm/min of transverse feed results in optimal process parameter combination for obtaining better values for tensile strength, microhardness and wear loss i.e. A3 B3 C3. The microstructure evaluation for fabricated and worn surfaces was studied using Scanning Electron Microscope (SEM).

Optimization of the Process Parameters on the Mechanical and Wear Properties of Al-SiC Nano-Composites Fabricated by Friction Stir Processing Using Desirability Approach

Modelling of peak temperature during friction stir processing of magnesium alloy AZ91

The ability to generate nano-sized grains is one of the advantages of friction stir processing (FSP). However, the high temperatures generated during the stirring process within the processing zone stimulate the grains to grow after recrystallization. Therefore, maintaining the small grains becomes a critical issue when using FSP. In the present reports, coolants are applied to the fixture and/or processed material in order to reduce the temperature and hence, grain growth. Most of the reported data in the literature concerning cooling techniques are experimental. We have seen no reports that attempt to predict these quantities when using coolants while the material is undergoing FSP. Therefore, there is need to develop a model that predicts the resulting grain size when using coolants, which is an important step toward designing the material microstructure. In this study, two three-dimensional computational fluid dynamics (CFD) models are reported which simulate FSP with and without coolant application while using the STAR CCM+ CFD commercial software. In the model with the coolant application, the fixture (backing plate) is modeled while is not in the other model. User-defined subroutines were incorporated in the software and implemented to investigate the effects of changing process parameters on temperature, strain rate and material velocity fields in, and around, the processed nugget. In addition, a correlation between these parameters and the Zener-Holloman parameter used in material science was developed to predict the grain size distribution. Different stirring conditions were incorporated in this study to investigate their effects on material flow and microstructural modification. A comparison of the results obtained by using each of the models on the processed microstructure is also presented for the case of Mg AZ31B-O alloy. The predicted results are also compared with the available experimental data and generally show good agreement.

Modeling the Effects of Coolant Application in Friction Stir Processing on Material Microstructure Using 3D CFD Analysis

Friction Stir Processing (FSP) has emerged as an effective tool for enhancing sheet metal properties through microstructural modification of processed materials. Despite the large number of studies, most of the work that has been done in the FSP field focuses primarily on experimental work. Only limited modeling attempts on temperature distribution and strain rate analysis have been conducted. In this work, a three dimensional Computational Fluid Dynamics (CFD) model was developed to simulate FSP using the STAR CCM+ CFD commercial software. User-defined subroutines were developed and implemented to investigate the effects of process parameters on temperature, strain rate, flow stress and material velocity fields in, and around, the processed nugget. In addition, a correlation between process parameters and the Zener-Holloman parameter was developed to predict the grain size distribution in the processed zone. Different stirring conditions were incorporated in this study to investigate their effects on material flow and microstructural modification. The modeling results were compared with the available experimental data and showed good agreement.

M. H. Ali

Papers

Modeling of friction stir processing using 3D CFD analysis