Showing papers on "Weldability published in 2014"

Effect of welding speed on microstructural and mechanical properties of laser lap weld joints in dissimilar Al and Cu sheets

Abstract: Conventional fusion welding of aluminium and copper dissimilar materials is difficult because of poor weldability arising from the formation of brittle intermetallic compounds on the weld zone as well as different chemical, mechanical and thermal properties of welded joints. Joining of Al and Cu plates or sheets offers a metallurgical challenge due to unavoidable formation of brittle intermetallic compounds. Therefore, it is necessary to effectively suppress the formation and growth of Al–Cu intermetallic compounds. For welding of dissimilar Al and Cu sheets, no systematic work has been conducted to reduce these defects. Thus, this paper focuses on the effect of welding speed on the quality of a lap weld joint in the Al and Cu sheets with a single mode fibre laser. It was found that consequently sound strong weld joints could be produced by suppressing the formation of intermetallic compounds in the interface zone at extremely high speeds.

Effects of surface coating on weld growth of resistance spot-welded hot-stamped boron steels

Abstract: Aluminum-silicon-based and zinc-based metallic coatings have been widely used for hot-stamped boron steel in automotive applications. In this study, resistance spot weldability was explored by investigating the effects of the properties of metallic coating layers on heat development and nugget growth during resistance spot welding. In the case of the aluminum-silicon-coated hot-stamped boron steel, the intermetallic coating transformed into a liquid film that covered the faying interface. A wide, weldable current range was obtained with slow heat development because of low contact resistance and large current passage. In the case of the zinc-coated hot-stamped boron steel, a buildup of liquid and vapor formation under large vapor pressure was observed at the faying interface because of the high contact resistance and low vaporization temperature of the intermetallic layers. With rapid heat development, the current passage was narrow because of the limited continuous layer at the faying interface. A more significant change in nugget growth was observed in the zinccoated hot-stamped boron steel than in the aluminum-silicon-coated hot-stamped boron steel.

Weldability and weld performance of candidate austenitic alloys for advanced ultrasupercritical fossil power plants

Abstract: Advanced ultrasupercritical steam conditions of up to 760°C and 34·5 MPa have been investigated in various programmes around the world over the last two decades. To date, much progress has been made, and three candidate materials, namely ferritic, austenitic and nickel base superalloys, have been investigated for high temperature strength, corrosion resistance and weldability. In an earlier published paper, welding and weldability of ferritic alloys were discussed. This paper considers the unique weldability characteristics for utilisation of austenitic stainless steels in future advanced ultrasupercritical fossil power plant designs and covers topics such as fundamentals of austenitic stainless steel welds, including weldability, filler metals and dissimilar metal welds, and discusses the prognosis for this class of materials for advanced ultrasupercritical fossil fired power plants.

Laser Engineered Net Shape (LENS) Technology for the Repair of Ni-Base Superalloy Turbine Components

Abstract: The capability of the laser engineered net shape (LENS) process was evaluated for the repair of casting defects and improperly machined holes in gas turbine engine components. Various repair geometries, including indentations, grooves, and through-holes, were used to simulate the actual repair of casting defects and holes in two materials: Alloy 718 and Waspaloy. The influence of LENS parameters, including laser energy density, laser scanning speed, and deposition pattern, on the repair of these defects and holes was studied. Laser surface remelting of the substrate prior to repair was used to remove machining defects and prevent heat-affected zone (HAZ) liquation cracking. Ultrasonic nondestructive evaluation techniques were used as a possible approach for detecting lack-of-fusion in repairs. Overall, Alloy 718 exhibited excellent repair weldability, with essentially no defects except for some minor porosity in repairs representative of deep through-holes and simulated large area casting defects. In contrast, cracking was initially observed during simulated repair of Waspaloy. Both solidification cracking and HAZ liquation cracking were observed in the repairs, especially under conditions of high heat input (high laser power and/or low scanning speed). For Waspaloy, the degree of cracking was significantly reduced and, in most cases, completely eliminated by the combination of low laser energy density and relatively high laser scanning speeds. It was found that through-hole repairs of Waspaloy made using a fine powder size exhibited excellent repair weldability and were crack-free relative to repairs using coarser powder. Simulated deep (7.4 mm) blind-hole repairs, representative of an actual Waspaloy combustor case, were successfully produced by the combination use of fine powder and relatively high laser scanning speeds.

Review of the weldability window concept and equations for explosive welding

Abstract: Explosive cladding/welding is usually considered a solid state process in which the detonation of a certain amount of an explosive composition is used to accelerate one of the materials to be weld against the other in order to promote a high velocity oblique collision that will be responsible for bonding the materials. The conditions that should be met to achieve good welds define what is called as a weldability window or criteria. A weldability criteria based on the collision point velocity (Vc) and on the collision angle (β) is the most used today. In the β-Vc space the weldability window is defined by four lines or limits. Despite of its wide used in explosive welding works, neither the concepts behind those limits neither the equations used to define them in the β-Vc space are particularly clear. Contradictory concepts, and equations with undefined variables or parameters, are commonly found in the literature. This paper aims to clarify those concepts and equations through an integrated description of the weldability limits and a reviewed presentation of the associated equations with the variables and parameters, including their units, clearly defined. The reviewed concepts and equations are then used for the description of the explosive weld of stainless steel to carbon steel in cylindrical configuration.

Weldability of S500MC Steel in Underwater Conditions

Abstract: Wet welding with the use of covered electrodes is one of the methods of underwater welding This method is the oldest, the most economic and the most versatile The main difficulties during underwater wet welding are: high cooling rates of the joint, the presence of hydrogen in the arc area and formation of hard martensitic structure in the weld These phenomena are often accompanied by porosity of welds and large number of spatters, which are more advanced with the increase of water depth In this paper result of non-destructive tests, hardness tests and metallographic observations of S500MC steel joints performed underwater are presented The weldability of 500MC steel at water environment was determined

Cold Metal Transfer Joining of Aluminum AA6061-T6-to-Galvanized Boron Steel

Abstract: Along with the development of automobile industry for lightweight vehicles, more and more advanced and ultrahigh strength steels (e.g., hot stamping steel) have been used for automotive applications. Making use of the high strength steels not only reduces the vehicle weight and air emissions but also improves crash safety. Meanwhile, aluminum alloys are one of the lightest structural materials, and they have been widely used in automotive industry due to their many attractive properties such as low density, high specific strength along with good damping capacity. Since both hot stamping steel and aluminum alloys are being widely used for automotive applications, joining of hot stamping steel to aluminum alloys is inevitable. In this study, the feasibility of joining aluminum alloy AA6061-T6 to galvanized boron steel by cold metal transfer (CMT) method using AA4043 filler metal was investigated. The microstructures and chemical compositions of the welded lap joints were examined using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), while the static strengths of the joints were measured. Test results showed that a sound weld-brazed joint which consisted of rich zinc zone, reaction interface zone, weld metal zone and fusion zone was formed. The phases and thickness of the reaction layers were analyzed and identified. In addition, the strength of CMT weld-brazed aluminum AA6061-T6 to galvanized boron steel depends on the torch deviation (i.e., distance between the welding torch and the edge of the weld seam). The joints fabricated with a deviation distance of 2 mm had greater strength than that of the joints made a deviation distance of 0 mm. Finally, the effect of temperature exposure of hot stamping on the weldability of CMT joining of joining aluminum AA6061-T6 to galvanized boron steel was investigated. It was found that the surface of galvanized boron steel was severely oxidized after heat treatment process and consequently reduced the weldability in CMT joining AA6061-T6 and galvanized boron steel.