This article reviews weldability of aluminum alloys and factors that affect weld performance. It first addresses hot tears, which can form during the welding of various aluminum alloys. It then presents comparison data from different weldability tests and discusses the specific properties that affect welding, namely oxide characteristics; the solubility of hydrogen in molten aluminum; and its thermal, electrical, and nonmagnetic characteristics. The article addresses the primary factors commonly considered when selecting a welding filler alloy, namely ease of welding or freedom from cracking, tensile or shear strength of the weld, weld ductility, service temperature, corrosion resistance, and color match between the weld and base alloy after anodizing. A number of factors, both global and local, that influence the fatigue performance of welded aluminum joints are also covered.

Stainless steel base metals and the welding filler metals used with them are chosen on the basis of suitable corrosion resistance for the intended application. This article describes several constitution diagrams that that have been developed to predict microstructures and properties. This is followed by discussions of weldability, cracking, and the engineering properties of stainless steel welds, namely martensitic stainless steels, ferritic stainless steel welds, austenitic stainless steels, and duplex stainless steels.

This article discusses the weldability and fusion weld properties of refractory metal alloys. The alloys discussed include tantalum, niobium, rhenium, molybdenum, and tungsten.

Ferritic stainless steels are essentially iron-chromium alloys with body-centered cubic crystal structures. Chromium content is usually in the range of 11 to 30%. The primary advantage of the ferritic stainless steels, and in particular the high-chromium, high-molybdenum grades, is their excellent stress-corrosion cracking resistance and good resistance to pitting and crevice corrosion in chloride environments. This chapter provides information on the classifications, properties, and general welding considerations of ferritic stainless steels. The emphasis is placed on intergranular corrosion, which is the most common cause of failure in ferritic stainless steel weldments. Two case histories involving intergranular corrosion failures of ferritic stainless steel weldments are included. A brief discussion on hydrogen embrittlement is also provided.

This article discusses the fusion welding processes that are most widely used for joining titanium, namely, gas-tungsten arc welding, gas-metal arc welding, plasma arc welding, laser-beam welding, and electron-beam welding. It describes several important and interrelated aspects of welding phenomena that contribute to the overall understanding of titanium alloy welding metallurgy. These factors include alloy types, weldability, melting and solidification effects on weld microstructure, postweld heat treatment effects, structure/mechanical property/fracture relationships, and welding process application.

This chapter discusses the various methods used to join titanium alloy assemblies, focusing on welding processes and procedures. It explains how welding alters the structure and properties of titanium and how it is influenced by composition, surface qualities, and other factors. It describes several welding processes, including arc welding, resistance welding, and friction stir welding, and addresses related issues such as welding defects, quality control, and stress relieving. The chapter also covers mechanical fastening techniques along with adhesive bonding and brazing.

This chapter covers the welding characteristics of titanium along with the factors that determine which welding method is most appropriate for a given application. It discusses the joinability of titanium alloys, the effect of heat on microstructure, the cause of various defects, and the need for contaminant-free surfaces and atmospheres. It describes common forms of fusion, arc, and solid-state welding along with the use of filler metals, shielding gases, and stress-relief treatments. It also discusses the practice of titanium brazing and the role of filler metals.

This article describes the weldability tests that are used to evaluate the effects of welding on such properties and characteristics as base-metal and weld-metal cracking; base-metal and weld-metal ductility; weld penetration; and weld pool shape and fluid flow. It also describes several weldability tests for evaluating cracking susceptibility, classified as self-restraint or externally loaded tests. The article discusses the processes, advantages, and disadvantages of the weld pool shape tests, the weld penetration tests, and the Gleeble test.

Failure analysis of steel welds may be divided into three categories. They include failures due to design deficiencies, weld-related defects usually found during inspection, and failures in field service. This chapter emphasizes the failures due to various discontinuities in the steel weldment. These include poor workmanship, a variety of hydrogen-assisted cracking failures, stress-corrosion cracking, fatigue, and solidification cracking in steel welds. Hydrogen-assisted cracking can appear in four common forms, namely underbead or delayed cracking, weld metal fisheyes, ferrite vein cracking, and hydrogen-assisted reduced ductility.

A brittle fracture occurs at stresses below the material's yield strength (i.e., in the elastic range of the stress-strain diagram). This chapter focuses on brittle fracture in metals and, more specifically, ferrous alloys. It lists the factors that must all be present simultaneously in order to cause brittle fracture in a normally ductile steel. The chapter then discusses the macroscale characteristics and microstructural aspects of brittle fracture. A summary of the types of embrittlement experienced by ferrous alloys is presented. The chapter concludes with a brief section providing information on mixed fracture morphology.

Nickel-base alloys used for low-temperature aqueous corrosion are commonly referred to as corrosion-resistant alloys (CRAs), and nickel alloys used for high-temperature applications are known as heat-resistant alloys, high-temperature alloys, or superalloys. The emphasis in this chapter is on the CRAs and in particular nickel-chromium-molybdenum alloys. The chapter provides a basic understanding of general welding considerations and describes the welding metallurgy of molybdenum-containing CRAs and of nickel-copper, nickel-chromium, and nickel-chromium-iron CRAs. It discusses the corrosion behavior of nickel-molybdenum alloys and nickel-chromium-molybdenum alloys. Information on the phase stability and corrosion behavior of nickel-base alloys is also included.

This article reviews the fundamental and specific factors that control the properties of steel weldments in both the weld metal and heat-affected zone (HAZ). The influence of welding processes, welding consumables, and welding parameters on the weldment properties is emphasized. The service properties of weldments in corrosive environments are considered and subjected to cyclic loading. The article summarizes the effects of major alloying elements in carbon and low-alloy steels on HAZ microstructure and toughness. It discusses the processes involved in controlling toughness in the HAZ and the selection of the proper filler metal. The article provides a comparison between single-pass and multipass welding and describes the effect of welding procedures on weldment properties and the effects of residual stresses on the service behavior of welded structures. It also describes the fatigue strength and fracture toughness of welded structures. The article reviews various types of corrosion of weldments.

This appendix provides reference tables listing weldability of cast irons, steels, and nonferrous metals. A process selection table for arc welding carbon steels is included, and recommended preheat and interpass temperature tables are also presented. This appendix includes information on qualification codes and standards.

The formation of defects in materials that have been fusion welded is a major concern in the design of welded assemblies. This article describes four types of defects that, in particular, have been the focus of much attention because of the magnitude of their impact on product quality. Colloquially, these four defect types are known as hot cracks, heat-affected zone microfissures, cold cracks, and lamellar tearing.

This article describes the repair of weld defects and failed structures. It provides information on three factors that must first be considered before attempting a repair, namely material weldability, nature of the failure that prompted the repair, and involvement of any code requirements. The article discusses the processes involved in welding process selection and the methods of preparing base metal for repair welding. It presents the guidelines for weld repairs of various ferrous (carbon steels, cast irons, and stainless steels) and nonferrous (for example, titanium) base metals.

This chapter discusses the causes and effects of ductile and brittle fracture and their key differences. It describes the characteristics of ductile fracture, explaining how microvoids develop and coalesce into larger cavities that are rapidly pulled apart, leaving bowl-shaped voids or dimples on each side of the fracture surface. It includes SEM images showing how the cavities form, how they progress to final failure, and how dimples vary in shape based on loading conditions. The chapter, likewise, describes the characteristics of brittle fracture, explaining why it occurs and how it appears under various levels of magnification. It also discusses the ductile-to-brittle transition observed in steel, the characteristics of intergranular fracture, and the causes of embrittlement.

Depending on the operating environment and the nature of the applied loading, a structure can fail by a number of different modes, including brittle fracture, ductile fracture, plastic collapse, fatigue, creep, corrosion, and buckling. These failure modes can be broken down into the categories of fracture, fatigue, environmental cracking, and high-temperature creep. This article discusses each of these categories, as well as the benefits of a fitness-for-service approach.

Nickel-base alloys are generally used in harsh environments that demand either corrosion resistance or high-temperature strength. This article first describes the general welding characteristics of nickel-base alloys. It then describes the weldability of solid-solution nickel-base alloys in terms of grain boundary precipitation, grain growth, and hot cracking in the heat-affected zone; fusion zone segregation and porosity; and postweld heat treatments. Next, the article analyzes the welding characteristics of dissimilar and clad materials. This is followed by sections summarizing the various types and general weldability of age-hardened nickel-base alloys. The article then discusses the composition, welding metallurgy, and properties of cast nickel-base superalloys. Finally, it provides information on the welding of dissimilar metals, filler metal selection for welding clad materials and for overlay cladding, service conditions during repair, and welding procedural idiosyncrasies of cobalt-base alloys.