Research Updates

Friction Stir Welding and Processing of A286 Alloy

There are many critical considerations in the tool selection for FSP of high strength materials. Two of these are weld quality and tool wear. Weld quality is dependent on heat generation and dissipation which is affected by tool properties. Temperatures reached in the workpiece depend on tool properties such as thermal conductivity and thermal expansion coefficient. Thermal conductivity determines the rate of heat removal and affects the temperature fields and flow stresses in the workpiece. Coefficient of thermal expansion affects thermal stresses of the tool.

Dissimilar Metal Friction Stir Welding

Use of multi-metal components in the automobile and other industries is increasing to utilize the weight saving factor of light metals and alloys to get higher fuel efficiency. Joining different metals is currently executed using mechanical fasteners or conventional welding techniques such as arc welding, laser welding, etc. Mechanical fasteners demand design improvement, machining, extra space for fasteners, etc. Conventional welding techniques develop defects and low strength welds due to the large differences in thermal and thermo-mechanical properties of the metals to be welded.

FSW Super Predictor

Development of friction stir technology is limited to rigorous experimental validation. Currently, process optimization and innovation is heavily dependent on the accumulated empirical experience retarding faster process development. Though experiments are critical to advance friction stir welding/processing (FSW/P), they need to be coupled with predictive modeling to accelerate the developmental process. Therefore the overall purpose of this project is to develop an integrated computational model with predictive capabilities.

Friction Stir Microstructural Modification for Fatigue

Fatigue performance of A356 cast aluminum alloy is limited by the presence of defects in the microstructure like casting porosities, non-metallic inclusions, non-uniform distribution of secondary phases, shape and morphology of particles, etc. The primary goal of this project is to improve the fatigue life of A356 alloy through microstructural modification by friction stir processing (FSP), with the aim of eventually developing high performance alloys for elevated temperature fatigue applications.

Friction Stir Welding of Al-Li Alloys

There is a high demand of light weight structural alloys, especially in the aerospace industry. Lithium, the lightest metallic element, addition offers weight saving advantages in aluminum based alloys. Addition of each 1% lithium in aluminum based alloy, reduces the density by 3% and increases the elastic modulus by 6%. Al-Li alloys offers high strength levels which are comparable to that of 7XXX high strength aluminum alloys.

Friction Stir Welding and Processing of Magnesium Alloys

The objective of this project was twofold: (i) to improve the nugget efficiency in a precipitation strengthened WE43 alloy and (ii) toughness. Friction stir welding (FSW) involves a complex interplay between strain, strain rate and thermal history. Therefore, a major thrust was laid on comprehending the microstructural evolution as a function of welding parameters and the initial microstructure. The overall goal was to understand the physical metallurgy of a WE43 alloy subjected to FSW.

Friction Stir Spot Welding of Mg Alloys

The objectives of this project were to achieve an optimum strength in friction stir spot welded (FSSW) Elpo and Alodine coated magnesium alloy AZ31 and evaluate the effect of coating layer on the mechanical property, hooking feature and microstructure evolution. The research focused on investigation of material flow behavior during spot welding and its effect on texture evolution, and exploration of the mechanisms for grain structure evolution.

Friction Stir Microstructural Modification

The project was aimed to improve the material properties by modifying the microstructure. As-cast Al-Si piston components were friction stir processed to break the Si particles. Further objective was to prepare surface composites by incorporating the ceramic powders in to aluminum alloys using friction stir processing.

Microstructural Analysi

e-nde algorithims for Friction Stir Welding

CFSP - Wichita State University - Two electronic Non-Destructive Evaluation (e-NDE) algorithms for Friction Stir Welding (FSW) have been successfully developed in collaboration with Wichita State University (WSU) and South Dakota School of Mines and Technology (SDSM&T). According to the Probability of Detection (POD) analysis based on the maximum-likelihood method, the e-NDE method gave significantly better detection performances compared to the conventional ultrasonic-phased-array and the X-ray techniques.

Robust Temperature Control

CFSP - Brigham Young University - Figure 1 shows a weld that started in RPM control mode then given a temperature command 51°C lower than the current temperature.   The overshoot was 29%, rise time 3.325 seconds, 10% settling time of 17.3 seconds and 1°C settling time of 29.5 seconds. After the 1°C settling time, the temperature was held at 425°C with a standard deviation of 0.717°C for non-filtered temperature and 0.312°C for filtered temperature.

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