S. Gao

Bio: S. Gao is an academic researcher from Shandong University. The author has contributed to research in topics: Materials science & Composite material. The author has an hindex of 1, co-authored 1 publications receiving 232 citations.

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure Copper Plates

Abstract: It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding. Thus, double-side friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates, and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed. It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min, while a nonuniform relatively thick intermetallic compound (IMC) layer is formed at the Al/Cu interface, resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass, and seriously deteriorates the mechanical properties of the joint. With the increase of welding speed to more than 300 mm/min void defects appear in the joint, but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface. The maximum tensile strength and elongation of Al/Cu weld are, respectively, 135.11 MPa and 6.06%, which is achieved at the welding speed of 400 mm/min. In addition, due to the influence of welding distortion of the first-pass weld, the second-pass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides. The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.

Study on the Actuating Performance of an Embedded Macro Fiber Composite Considering the Shear Lag Effect

Abstract: Macro fiber composite (MFC), which are new ultrathin piezoelectric smart materials, are mostly applied in the fields of shell structure deformation and vibration control. Among others, the application of embedded MFCs in sandwich structures has received wide attention. Currently, its actuating force formula is primarily acquired based on the Bernoulli–Euler Model, which does not consider the shear lag effect and actuating force of MFC ends. To study the actuating performance of an MFC in a sandwich structure, according to its action characteristics, the MFC is divided into upper and lower actuating units without any interaction between to two under the condition of plane strain, and the shear lag effect is considered between the units and the top and bottom of the sandwich structure. The actuating force of the MFC ends is obtained by considering its influence on the bending deformation of the sandwich structure, which deduces the actuating force formula of the embedded MFC. In contrast to ANSYS piezoelectric simulation, the distribution of the MFC interior normal stress is similar to the result from ANSYS piezoelectric simulation, and there is a very small deviation between the MFC end and central normal stress and the result from ANSYS piezoelectric simulation. Taking the end deflection of the sandwich structure with an embedded MFC as an example, the actuating force simulation of the MFC considering the shear lag effect is compared with the ANSYS piezoelectric simulation and actuating force simulation based on the Bernoulli–Euler model. The result indicates that the actuating force simulation of the MFC considering the shear lag effect is closer to the ANSYS piezoelectric simulation, which proves the rationality and necessity of considering the shear lag effect and end actuating force of the MFC.

Recent Development in Friction Stir Processing as a Solid-State Grain Refinement Technique: Microstructural Evolution and Property Enhancement

Abstract: Increasing demand of lightweight structures with exceptional properties elicits materials processing and manufacturing technologies to tailor blanks in order to achieve or enhance those pre...

Friction Stir Processing of Magnesium Alloys: A Review

Abstract: Magnesium (Mg) alloys have been extensively used in various fields, such as aerospace, automobile, electronics, and biomedical industries, due to their high specific strength and stiffness, excellent vibration absorption, electromagnetic shielding effect, good machinability, and recyclability. Friction stir processing (FSP) is a severe plastic deformation technique, based on the principle of friction stir welding. In addition to introducing the basic principle and advantages of FSP, this paper reviews the studies of FSP in the modification of the cast structure, superplastic deformation behavior, preparation of fine-grained Mg alloys and Mg-based surface composites, and additive manufacturing. FSP not only refines, homogenizes, and densifies the microstructure, but also eliminates the cast microstructure defects, breaks up the brittle and network-like phases, and prepares fine-grained, ultrafine-, and nano-grained Mg alloys. Indeed, FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity. Furthermore, FSP can produce particle- and fiber-reinforced Mg-based surface composites. As a promising additive manufacturing technique of light metals, FSP enables the additive manufacturing of Mg alloys. Finally, we prospect the future research direction and application with friction stir processed Mg alloys.

Friction Stir Welding of Dissimilar Aluminum Alloy Combinations: State-of-the-Art

Abstract: Friction stir welding (FSW) has enjoyed great success in joining aluminum alloys. As lightweight structures are designed in higher numbers, it is only natural that FSW is being explored to join dissimilar aluminum alloys. The use of different aluminum alloy combinations in applications offers the combined benefit of cost and performance in the same component. This review focuses on the application of FSW in dissimilar aluminum alloy combinations in order to disseminate research this topic. The review details published works on FSWed dissimilar aluminum alloys. The detailed summary of literature lists welding parameters for the different aluminum alloy combinations. Furthermore, auxiliary welding parameters such as positioning of the alloy, tool rotation speed, welding speed and tool geometry are discussed. Microstructural features together with joint mechanical properties, like hardness and tensile strength measurements, are presented. At the end, new directions for the joining of dissimilar aluminum alloy combinations should guide further research to extend as well as to improve the process, which is expected to raise further interest on the topic.

Additive manufacturing method and different welding applications

Abstract: Additive manufacturing (AM) technology, in other words “layered manufacturing” or “3D printer technology” has been developing rapidly in recent years. Unlike the traditional manufacturing method (TM), the working principle of AM technology is to create layer-based production by deposition the layers on top of each other. Owing to its advantages such as material saving, lower cost, the ability to produce parts without the need for molds and the design flexibility in complex shaped parts, it has brought a breath of fresh air to the areas where it is used primarily medical, aerospace and automotive. However, the parts produced by AM method have dimensional limitations. According to recent studies, in order to eliminate this problem, metal materials produced with AM can be combined with commonly used by different welding methods so that large parts can be obtained. In this study, these welding methods are explained and recent researches are examined. AM technology and methods are introduced. The usage areas of the method are described. In addition, the welding parameters and the effects of this new method on the mechanical properties and microstructures are investigated.