Friction stir welding (FSW), a highly efficient solid-state joining technique, has been termed as “green” technology due to its energy efficiency and environment friendliness. It is an enabling technology for joining metallic materials, in particular lightweight high-strength aluminum and magnesium alloys which were classified as unweldable by traditional fusion welding. It is thus considered to be the most significant development in the area of material joining over the past two decades. Friction stir processing (FSP) was later developed based on the basic principles of FSW. FSP has been proven to be an effective and versatile metal-working technique for modifying and fabricating metallic materials. FSW/FSP of aluminum alloys has prompted considerable scientific and technological interest since it has a potential for revolutionizing the manufacturing process in the aerospace, defense, marine, automotive, and railway industries. To promote widespread applications of FSW/FSP technology and ensure t...

Recent Advances in Friction Stir Welding/Processing of Aluminum Alloys: Microstructural Evolution and Mechanical Properties

Aluminium alloys AA 5083 and AA 6082 have been friction stir welded and the mechanical properties and microstructures of the welds have been evaluated. Alloy AA 5083 mainly fractured near t...

Microstructure and mechanical properties of friction stir welded aluminium alloys with special reference to AA 5083 and AA 6082

Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging, building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry. Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows: grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.

A Review on Grain Refinement of Aluminum Alloys: Progresses, Challenges and Prospects

The superplastic properties and microstructural evolution of a 0.2% Zr and 1.6% Mn modified 5083 aluminum alloy with an initial grain size of 6.2 μm were examined at strain rates ranging from 10−5 to 10−1 s−1 in the temperature interval 500–580 °C. The maximum elongation-to-failure of 1150% was found at 570 °C, which is near the solidus temperature of 572 °C, and an initial strain rate of 2.8×10−3 s−1. The corresponding strain rate sensitivity coefficient, m, was about 0.6. It was shown that increasing the temperature from 550 to 570 °C results in reduced cavitation and expanding the optimal interval of superplasticity toward lower strain rates due to the disappearance of the threshold stress. The influence of temperature on the mechanisms of superplastic deformation is discussed.

Superplastic behavior of an Al/Mg alloy at elevated temperatures

The mechanical properties and microstructural features of aluminum 5083 (AI5083) weldments processed by gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) are investigated. Weldments processed by both methods are mechanically softer than the parent material AI5083, and could be potential sites for plastic localization. It is revealed that AI5083 weldments processed by GTAW are mechanical more reliable than those by GMAW. The former bears higher strength, more ductility, and no apparent microstructure defects. Perceivable porosity in weldments by GMAW is found, which could account for the distinct mechanical properties between weldments processed by GTAW and GMAW. It is suggested that caution should be exercised when using GMAW for AI5083 in the high-speed-train industry where such light weight metal is broadly used.

Microstructure and mechanical properties of aluminum 5083 weldments by gas tungsten arc and gas metal arc welding

A preliminary investigation of thermomechanical processing of 5083 aluminum plate (Al-4.7%Mg-0.7%Mn) was undertaken to develop a fine-grain sheet for superplastic forming applications. Significant differences in grain size and the extent of superplasticity are seen in hot-rolled vs. cold-rolled sheets, with tensile elongations exceeding 600% for the cold-rolled alloy. Additionally, a separate fine-grain sheet of the same alloy, produced by Alusuisse Co., was studied in greater detail. Superplastic deformation behavior of this sheet was investigated under uniaxial tension over the temperature range of 500–565 °C. Strain rate sensitivity values greater than 0.3 were observed over a strain rate range of (3 × 10−5)–(1 × 10−2) s−1 with a maximum value of 0.65 obtained for strain rate of 5 × 10−4 s−1 at 565 °C. Constant-velocity tension tests consistently show larger strains to failure and lower strain hardening rate than the corresponding “constant-strain-rate” tests for the range investigated. A short but rapid prestraining step, prior to the normal superplastic straining, produced enhanced tensile elongation at all temperatures. Under the two-step schedule, a maximum tensile elongation of 600% was obtained at 550 °C, which was regarded as the optimum superplastic temperature under this condition. This paper and a companion paper are used to provide the details of results obtained to date from this study.

Grain refinement and superplasticity in 5083 Al

The commonly used thin-slice fiber push-out or pull-out tests to measure interface properties of fiber-reinforced metal-matrix composites can introduce biaxial bending of metallic matrix around the fiber and generate complex interfacial stress states. These factors complicate the interpretation of results from these tests. Also, the results from a single fiber push-out (or pull-out) test might not directly relate to the shear properties associated with an assemblage of fibers as in an actual composite body. In this paper, a technique has been presented in which a model, single-ply multi-fiber composite specimen is tested in a state of nearly pure shear. The chief advantages of this technique are that specimen preparation and test methodology are simplified, and the influence of non-shear stresses, such as those associated with the fiber push-out or pull-out test, are minimized. Composite shear strength has been measured as a function of fiber packing density. A method of interpreting the shear strength data, which includes contributions from fiber-matrix debonding strength as well as shear fracture strength of the matrix, has been developed. The method permits measurement of the interfacial shear strength and an assessment of matrix residual stress generated due to CTE difference between the matrix and the fiber. The method has been used to study the effect of surface coatings on SiC fiber, e.g. C-rich coating (SCS-6) and TiN coating, on the interfacial strength in Ti-1100/SiC fiber composites. Microstructures and interface chemistries of as-fabricated composites and sheared composite surfaces are also presented.

R. Verma

Papers

Grain refinement and superplasticity in 5083 Al

Measurement of interfacial shear properties of composites of Ti-1100 alloy reinforced with SCS-6 SiC monofilament fiber