Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints

Friction stir welding was employed to weld dissimilar 2219/5A06 Al alloys in this work. The influences of alloy positioning on the mechanical properties and fracture behavior of the joints were studied via fracture morphology observation and microstructural analysis. The results show that the difference in the plastic flow and thermal field in the welding process is caused by different basic material configurations, which results in the formation of a free strengthening phase zone and microstructural heterogeneity in the joint. The low-hardness texture component caused by the free strengthening phase zone and microstructural heterogeneity becomes crack initiation, and a crack tends to propagate along the grain boundaries. Finally, when the stronger 2219-T6 alloy was placed on the advancing side, the joints had better tensile properties. The average tensile strengths of the 2A5R and 5A2R joints can reach 79.8% (343 MPa) and 78.4% (337 MPa) of the 2219 base material, respectively

Effect of Ultrasonic Vibration in Friction Stir Welding of 2219 Aluminum Alloy: An Effective Model for Predicting Weld Strength

Friction stir welding (FSW) is today used as a premier solution for joining non-ferrous metals, although there are many limitations in its application. One of the objectives of this study was to propose an innovative welding technique, namely ultrasonic-assisted friction stir welding (UAFSW) with longitudinal ultrasonic vibration applied to the stirring head. In this paper, UAFSW mechanical properties and microstructure analysis were performed to demonstrate that the fluidity of the weld area was improved and the strengthened phase organization was partially preserved, due to the application of ultrasonic vibration. The addition of 1.8 kW of ultrasonic vibration at 1200 rpm and 150 mm/min welding parameters resulted in a 10.5% increase in the tensile strength of the weld. The ultimate tensile strength of 2219 aluminum alloy UAFSW was analyzed and predicted using mathematical modeling and machine learning techniques. A full factorial design method with multiple regression, random forest, and support vector machine was used to validate the experimental results. In predicting the tensile behavior of UAFSW joints, by comparing the evaluation metrics, such as R2, MSE, RMSE, and MAE, it was found that the RF model was 22% and 21% more accurate in the R2 metric compared to other models, and RF was considered as the best performing machine learning method.</jats:p

Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints

Friction stir welding was employed to weld dissimilar 2219/5A06 Al alloys in this work. The influences of alloy positioning on the mechanical properties and fracture behavior of the joints were studied via fracture morphology observation and microstructural analysis. The results show that the difference in the plastic flow and thermal field in the welding process is caused by different basic material configurations, which results in the formation of a free strengthening phase zone and microstructural heterogeneity in the joint. The low-hardness texture component caused by the free strengthening phase zone and microstructural heterogeneity becomes crack initiation, and a crack tends to propagate along the grain boundaries. Finally, when the stronger 2219-T6 alloy was placed on the advancing side, the joints had better tensile properties. The average tensile strengths of the 2A5R and 5A2R joints can reach 79.8% (343 MPa) and 78.4% (337 MPa) of the 2219 base material, respectively.</jats:p

Microstructure and Mechanical Characterization of a Dissimilar Friction-Stir-Welded CuCrZr/CuNiCrSi Butt Joint

Dissimilar CuNiCrSi and CuCrZr butt joints were successfully frictionstirwelded at constant welding speed of 150 mm/min and rotational speed of 1400 rpm with the CuCrZr alloy or the CuNiCrSi alloy located on the advancing side (AS). The microstructure and mechanical properties of joints were investigated. When the CuCrZr alloy was located on the AS, the area of retreating material in the nugget zone was a little bigger. The Cr solute-rich particles were found in the nugget zone on CuCrZr side (CuCrZr-NZ) while a larger density of solute-rich particles identified as the concentration of Cr and Si element was found in the nugget zone on CuNiCrSi side (CuNiCrSi-NZ). The Cr precipitates and &delta;-Ni2Si precipitates were found in the base metal on CuNiCrSi side (CuNiCrSi-BM) but only Cr precipitates can be observed in the base metal on CuCrZr side (CuCrZr-BM). Precipitates were totally dissolved into Cu matrix in both CuCrZr-NZ and CuNiCrSi-NZ, which led to a sharp decrease in both micro-hardness and tensile strength from BM to NZ. When the CuNiCrSi was located on the AS, the tensile testing results showed the fracture occurred at the CuCrZr-NZ, while the fracture was found at the mixed zone of CuNiCrSi-NZ and CuCrZr-NZ for the other case

A novel slip rate model for determining the interfacial contact state in friction stir welding

Slip rate is a key parameter that represents the interfacial contact state between the tool and the workpiece, and it determines the heat generated during friction stir welding (FSW). However, it is difficult to experimentally measure this interfacial field, and the actual contact state is quite unclear. Therefore, an advanced slip rate model is needed to determine the contact state and to accurately elucidate the heat generation mechanism in FSW. In this paper, a novel model is proposed to directly calculate the slip rate based on welding parameters; this model is established by conducting parametric inversion on the slip rate through finite element analysis. The results show that the slip rate increases with increasing welding speed and decreases with increasing rotational speed. Furthermore, the slip rate model reveals the impacts of the welding parameters on the interfacial contact state. When n/v is greater than 4.6, the dominant mode of heat generation is sticking friction in FSW. Conversely, the major mode of heat generation is sliding friction. A finite element model is used to investigate the thermal process and the distribution characteristics of the temperature field during FSW of 2219 aluminum alloy. The temperature field in the weld zone presents a ''bowl-shaped'' distribution, with the temperature at the top being higher than that at the bottom. Moreover, the temperature peak occurs at half the radius of the shoulder. The above results provide an important reference for understanding the heat generation mechanism and temperature history during FSW of aluminum alloys

Study of the Microstructure Evolution and Properties Response of a Friction-Stir-Welded Copper-Chromium-Zirconium Alloy

In this article, the copper-chromium-zirconium (CuCrZr) alloys plates with 21 mm in thickness were butt joined together by means of FSW (friction stir welding). The properties of the FSW joints are studied. The microstructure variations during the process of FSW were investigated by optical microscopy (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the grains size in the nugget zone (NZ) are significantly refined, which can be attributed to the dynamic recrystallization (DRX). The microstructure distribution in the NZ is inhomogeneous and the size of equiaxed grains are decreased gradually along the thickness direction from the top to bottom area of the welds. Meanwhile, it is found that the micro-hardness and tensile strength of the welds are slightly increased along the thickness direction from the top to the bottom area of the welds. All the nano-strengthening precipitates in the BM are dissolved into the Cu matrix in the NZ. Therefore, the decreases in hardness, tensile strength, and electrical conductivity can be attributed to the comprehensive effect of dissolution of nano-strengthening precipitates into the supersaturation matrix and severe DRX in the welded NZ