Analytical Modeling of Strain Rate Distribution During Friction Stir Processing

Friction stir processing (FSP) is an emerging method for improving surface properties of materials by composite fabrication. This study aims at optimizing the major FSP parameters and analysis of their real-time influence on the mechanical performance of a surface composite fabricated with Magnesium (Mg) matrix and Titanium Carbide (TiC) as reinforcement. Effects of different process parameters, tool rotational speed, plunge depth, the linear speed of the tool, cooling condition, and number of FSP passes have been examined. Using L27 array, a total of 27 combinations of these process parameters were analyzed by taking microhardness as an output response to find influential parameters by Taguchi's technique. Maximum micro-hardness was achieved when tool rpm of 600, cooling temperature of -10o C, tool feed of 15 mm/min, plunge depth of 0.35 mm, and 3 passes of FSP tool were chosen with the help of Taguchi's method. Analysis of variance indicated that cooling temperature, the tool feed, and the number of passes of the FSP tool were the most significant parameters.

As a noble surface modification technique, friction stir processing (FSP) has been established based on the principle of friction stir welding that refines the microstructure and localized plastic deformation of the material. Nevertheless, despite notable technological progress, challenges persist in utilizing FSP to improve material characteristics. This review paper offers a concise overview, summarizing the influence of process parameters on the microstructure mechanical and tribological properties of aluminium alloy subjected to FSP. In particular, the performance of aluminium alloy is discussed about FSP factors such as tool travel speed, rotating speed, reinforcement particles, multiple passes and tool tilt angle. This paper also reviewed the effect of different process parameters on the wear properties, corrosion and tribological characteristics of the processed alloy, which will facilitate researchers and business organizations in creating the needed upgraded composite.

The current study aims to provide a comprehensive explanation of metal matrix composite fabrication using various combinations of reinforcements and the principles of friction stir technique, as well as the impact of input processing parameters on mechanical properties performed by various researchers. The researchers sought to establish a link between the parameters of the input process and the output replies. Friction stir welding and processing consumes a lot less energy than other methods. Metal matrix composites have replaced traditional materials in many technical applications due to their unique mechanical and metallurgical qualities, stability, durability, and corrosion resistance. The friction stir method has a significant influence on the mechanical characteristics of manufactured composite surfaces due to process parameters such as rotating speed, tilt angle, feed, and deposition rate. The boost in diverse characteristics in surface composites has been brought forth by the solid-state nature of the processing procedure. Mechanical qualities are also influenced by the pin profile. The most common pin profiles are triangular, cylindrical, hexagonal, and pentagonal. On surface composites, the current work may provide a notion of defect-free welds with greater and enhanced mechanical characteristics.

Friction stir processed Ti‐6Al‐4V alloys are successfully prepared under low rotation speed (≤200 rpm) and low traverse speed (≤50 mm min−1). The microstructure of the stir zone is homogeneous in thickness. Effects of process parameters on microstructure and texture evolution of α‐Ti in the stir zone during friction stir processing are clarified. It is found that traverse speed had a significant impact on microstructure in the stir zone. The equiaxed nano‐crystalline α‐Ti grains without texture formed via friction stir processing below β transus. The high temperature range and severe deformation range are overlapped when the samples are processed with low traverse speed. Dynamic recrystallization happened repeatedly and fast cooling inhibited grain growth when the stir tool moved away the stir zone. Ti‐6Al‐4V alloy shows shear texture after friction stir processing below β transus with higher traverse speed. β → α transformation occurred and lamellar α colonies formed during cooling stage above β transus when the rotation and traverse speed are increased. The microstructure morphology and texture strength of Ti‐6Al‐4V plates could be regulated by combining of heating and cooling stages during friction stir processing.

Material flows during friction stir processes are very complex and not fully understood. Although the most literature reviews are presenting for material flow path, but Modified Friction Stir Channeling (MFSC) is a novel process based on Friction Stir Processing (FSP), which is being utilized to produce internal channel in Monolithic plates. A new flow pattern, in this study, is proposed to investigate material flow path and channel formation mechanism. The validity of this model is demonstrated by observing the cross-section and created keyhole using stop-action technique. The main difference between Friction Stir Channeling (FSC) and MFSC is the tilt angle. The effect of tilt angle and process parameters such as rotational speed and traverse speed on material flow path is studied. The results indicate that the tilt angle is an effective factor on forging of material behind of pin in the Advancing Side (AS) and also in the upper portion of channel roof imperfections. The rotational speed is an effective parameter on extruded material around the tool pin body and the extracted material in front of tool pin, because of the changing in the slip–stick condition and generated heat by tool. Traverse speed was an effective parameter on forging action of material and to keep material nearby tool pin in the behind of pin.

Mg–3·99Y–3·81Nd–0·53Zr (WE43) casting alloy was subjected to friction stir processing (FSP) at a constant rotation rate of 800 rev min−1 and various processing speeds of 30, 60, 90 and 120 mm min−1, and microstructures and mechanical properties of the experimental materials were investigated. With the processing speeds increasing, the average grain size first decreases and then increases, and the finest microstructure (∼2 μm) is prepared at the processing speed of 60 mm min−1. Owing to much finer microstructure, the mechanical properties of the WE43 alloy after FSP are significantly improved. The maximum tensile strength and elongation of the FSP WE43 alloy obtained at 60 mm min−1 are 290 MPa and 17·2% respectively. The fracture morphology shows that fine dimples and tearing edges can be observed on the FSP specimens. In addition, high temperature tensile tests show that the FSP WE43 alloys exhibit excellent high strain rate superplasticity, with a large elongation of 631% at 748 K at a strain rate of 2×10−2 s−1.

Experimental Investigation on Hybrid Friction Stir Processing using compressed air in Aluminum 7075 alloy

Low density of magnesium-based alloy is one potential as the lightest structural material for light weight-high strength applications for automotive and aerospace. Severe plastic deformation (SPD) together with thermomechanical processing are proved to be a successful method for attaining desired microstructural modifications through achieving fine and highly misoriented microstructures and creating various structures to the bulk properties of magnesium alloy. The material's deformation can result in an altered microstructure that is gainful to the material's requirements. However, the poor deformability of magnesium and its alloys limits the application of the thermomechanical approach. Controlling over temperature and deformation rate is hard to achieve. Among the thermomechanical processes, friction stir processing (FSP) offers an easy way to achieve process stability and mechanical properties enhancement by heat treatment which results in the closure of porosity and refined grain size. During this process, heat is generated by the rotation of the FSP processing tool. Few process parameters such as rotational and traverse speeds should be controlled to make FSP stay within the defined processing condition. It is critical to set the right tool rotational speed as well as traverse speed to ensure adequate heat generation. As there are no established standards for operating the FSP, the only solution is to experiment with different settings to find the best parameter which will produce better quality on processed magnesium alloy workpiece. This paper explores earlier studies on surface modification via FSP technique to improve the mechanical properties strengthening of magnesium alloy mainly on grain size and hardness. The surface modification was done mostly on popular series of magnesium alloy (AZ series) using different tool material, tool geometry and different parameters combination. A comprehensive view of surface modification on magnesium alloys which includes the FSP tool and workpiece material used, variations of FSP parameters settings as well as the effect on hardness and microstructure analysis will be discussed.

The cast Al-Zn-Mg 7000 alloy has become one of the most potential structural materials in many engineering fields such as aircraft body, automotive casting due to their high strength to weight ratio, strong age hardening ability, competitive weight savings, attractive mechanical properties and improvement of thermal properties. The cast aluminium alloy has been modified of surface layer through a solid-state technique is called friction stir process (FSP). But basic principle has been followed by friction stir welding (FSW). This process can be used to locally refine microstructures and eliminate casting defects in selected locations, where mechanical properties improvements can enhance component performance and service life. However, some specified process parameters have adopted during experimental works. Those parameters are tool rotation speed (720 rpm), plate traverse speed (80 mm/min), axial force (15 kN), and tool design (i.e., pin height 3.5 mm and pin diameter 3.0 mm), respectively. The main mechanism behind this process likely to axial force and frictional force acting between the tool shoulder and workpiece results in intense heat generation and plastically soften the process material. The specified ratio of rotational speed (720 rpm) to traverse speed (80 mm/min) is considered 9 as low heat input during FSP and its entails low Zn vaporization problem results as higher fracture toughness of aluminium alloy. It is well known that the stirred zone (SZ) consists of refine equiaxed grains produced due to dynamic recrystallization. FSP has been proven to innovatively enhancing of various properties such as formability, hardness and fracture toughness (32.60 MPa√m). The hardness and fracture toughness of double passes AC+FSP aluminium alloy had been investigated by performing Vicker’s hardness measurement and fracture toughness (KIC)(ASTM E-399 standard) tests. Detailed observations with optical microscopy, Vicker’s hardness measurement, SEM, TEM, and DTA analysis have conducted to analyse microstructure and fracture surfaces of double passes FSP aluminium alloy.

A bottom-up approach for optimization of friction stir processing parameters; a study on aluminium 2024-T3 alloy

Effect of Process Parameters and Tool Geometry on Fabrication of Ni Particles Reinforced 5083 Al Composite by Friction Stir Processing

4 - Mechanical properties

Friction stir processing is a newer technique for fabrication of surface composites. Surface composite fabrication by friction stir processing is simpler and offer many advantages as compared to conventional techniques. However, there are many challenges in composite fabrication due to asymmetric material flow and formation of defects. Reinforcement strategies, process parameters and reinforcement properties are key factors in fabrication of surface composites. In this study a newer reinforcement strategy is utilized to fabricate surface composites by pre-mixing the reinforcement particles with base alloy powders. The pre-mixing of ceramic reinforcement particles with metallic base alloy powder enhances the material flow and favours the uniform distribution of reinforcement particles.

: Focus: HOPE (FH) has developed the process parameters to successfully join AA6061 aluminum alloy and High Hardness Armor (HHA) steel using the friction stir process (FSP). Metallographic analysis conducted at the FH metallurgical laboratory, and later at the TARDEC metals lab, has confirmed that the dissimilar metals were metallurgically bonded at the joint surface with a thin (2-5 microns) Al-Fe intermetallic present. Mechanical load testing determined that the bimetallic FSP joint was stronger than similar AA6061-to-AA6061 fusion-welded and FSP joints. Initial process parameter trials were conducted to define the operating envelop for this FSP application. FH then evaluated the friction stir process parameters using an orthogonal array methodology. The parameters studied included tool rotation speed, tool traverse rate, tool tilt angle, plunge tool rotation speed, plunge rate, dwell, and joint offset. Other factors that were evaluated include tool design, fixture cooling, and auxiliary induction heating. In total 123 sets of process parameters were evaluated. Using the process parameter set which exhibited the greatest tensile strength FH produced a series of joint coupons which were then machined into test specimens for mechanical characterization. Metallographic samples were also prepared and analyzed using optical microscopy, scanning electron microscopy (SEM), electron back scatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). This report also includes a description of the induction pre-heating system that was designed and demonstrated during this project for the potential use for FSP of high hardness metal alloys.

The effect of process parameters on forming forces in single point incremental forming