This article summarizes the fatigue and fracture resistance of selected magnesium alloys. It reviews the effects of surface condition and test variables on fatigue strength. The article also provides an overview of the fatigue crack growth, fracture toughness, and stress-corrosion cracking of magnesium alloys.

Fracture mechanics is a multidisciplinary engineering topic that has foundations in both mechanics and materials science. This article summarizes the microstructural aspect of fracture resistance in structural materials. It provides a discussion on basic fracture principles and schematically illustrates the mechanism of crack propagation. The article describes the fracture resistance of high-strength steels, aluminum alloys, titanium alloys, and composites such as brittle matrix-ductile phase composites and metal-matrix composites. It also lists the effects of microstructural variables on fracture toughness of steels, aluminum alloys, and titanium alloys.

This article reviews general trends in the cyclic response for representative commercial alloys to establish the spectrum of cyclic properties attainable through microstructural alteration. Individual alloy classes are examined in detail to assess the understanding of relationships between microstructure and fatigue resistance. These alloys classes include ferritic-pearlitic alloys, martensitic alloys, maraging steels, and metastable austenitic alloys. The article also discusses the role of internal defects and selective surface processing in influencing fatigue performance.

Cr-Mo steels are preferred in the construction of high-temperature components because they possess excellent strength, toughness, and corrosion resistance relative to carbon steels and most low-alloy steels. This article discusses the composition and metallurgy of the heat-resistant Cr-Mo steels. It details the Charpy V-notch (CVN) toughness properties of Cr-Mo steels relevant to fatigue and fracture resistance. The fracture mechanics of Cr-Mo steels are reviewed. The article analyzes the characterization of low-cycle fatigue based on fatigue damage calculations. It concludes with information on fatigue crack growth and fatigue behavior of weldments.

The process of fatigue failure consists of three stages: initial fatigue damage leading to crack initiation; crack propagation to some critical size; and final, sudden fracture of the remaining cross section. Variations in mechanical properties, composition, microstructure, and macrostructure, along with their subsequent effects on fatigue life, have been studied extensively to aid in the appropriate selection of steel to meet specific end-use requirements. The metallurgical variables having the most pronounced effects on the fatigue behavior of carbon and low-alloy steels are strength, ductility, cleanliness, residual stresses, surface conditions, and aggressive environments. The article discusses the stress-based and strain-based approach to fatigue. The application of fatigue data in engineering design is complicated by the characteristic scatter of fatigue data; variations in surface conditions of actual parts; variations in manufacturing processes such as bending, forming, and welding; and the uncertainty of environmental and loading conditions in service.

Resistance welding (RW) encompasses many variations on the basic theme of local Joule heating while an external pressure is applied. This article provides an overview of the most generally applied RW processes, followed by a discussion on the general design aspects of various resistance-welded joints. The various resistance-welded joints include spot welds, projection welds, seam welds, and butt welds. The article explains the relative contributions of the Joule, Peltier, and Thomson effects for typical RW scenarios. It concludes with information on the electrode “follow” behavior.

This article provides an overview of the components of a resistance welding machine. It focuses on the single-phase control system and medium-frequency direct current system of resistance welding. The article also includes information on their feedback systems, rectification systems, and power sources.

This article describes the process applications, advantages, and limitations of resistance seam welding. The fundamentals of lap seam welding are also reviewed. The article details the types of seam welds, namely, lap seam welds and mash seam welds, and the processing equipment used for lap seam welding. The primary factors used to determine the selection of electrodes, including alloy type and wheel configuration, are reviewed. The article also describes weld quality and process control procedures.

This article provides a fundamentals-based description of solid-state resistance projection welding. It details simple analytical tools to understand the variety of mechanisms that occur during resistance projection welding. Factors relating to the quality of solid projection are discussed, in addition to an explanation of the mechanisms of bonding for solid projection welding. The article reviews how these mechanisms are affected by heat balance, current profile, and mechanical characteristics of the welding equipment. It also presents the design of projection welding mechanical systems.

Resistance spot welding (RSW) is the most widely used joining technique for the assembly of sheet metal products. This article discusses the process description, evaluation methods, and applications of RSW. It describes the equipment needed for RSW and explicates the major functions of electrodes in RSW and effect of surface condition on the technique. The article concludes with information on the safety precautions to be followed during the welding process.

This article presents the structural attributes and internal characteristics of spot welds as well as the commonly inspected imperfections in resistance welds. It describes the industrial requirements for weld quality. Commonly performed destructive evaluations, namely, manual testing, quasi-static mechanical tests, dynamic mechanical tests, and metallographic examination, are reviewed. The article reviews weld-quality monitoring using various process signals and provides a discussion on the on-line and off-line nondestructive evaluation methods of spot weld quality.

This article describes the significance of the three variables that affect the resistance spot welding process: welding current, electrode force, and welding time. It presents the effects of weld spacing and surface preparation on weld quality. The article elaborates the typical sequence of steps for determining the satisfactory conditions for spot welding and the mechanical aspects that affect this process. It considers the effects of process variables on the weld lobe. The article reviews surface preparation, part fit-up, electrode drives, weld parameters, and tests associated with seam welding. It concludes with a discussion on the welding equipment and other factors associated with resistance spot and seam welding.

Electrical resistance alloys include those types used in instruments, control equipment, heating elements, and devices that convert heat generated to mechanical energy. This article discusses the basic classification of electrical resistance alloys (resistance alloys, heating alloys, and thermostat metals), their subtypes, properties, service life, and operating temperatures. It describes the designing and fabrication of open resistance and sheathed heaters. The article contains a collection of tables and graphs that provide information on the mechanical properties, chemical composition, temperature coefficient of resistance, furnace operating temperatures, length and spacing of loops, ribbon size, and electrical capacity of heating elements.

This article reviews various test methods used for evaluating the corrosion resistance of powder metallurgy stainless steels. These include immersion testing, salt spray testing, and electrochemical testing. The article discusses the factors that affect corrosion resistance of sintered stainless steels: compaction-related factors, sintering-related factors, and effects of alloy composition. Corrosion resistance data for sintered stainless steels is provided.

This article provides a background of the complex relationship between titanium and its alloys with aqueous environments, which is dictated by the presence of a passivating oxide film. It describes the corrosion vulnerability of titanium and titanium oxides by the classification of oxide failure mechanisms. The mechanisms are spatially localized oxide film breakdown by the ingress of aggressive anions; spatially local or homogenous chemical dissolution of the oxide in a strong reducing-acid environment; and mechanical disruptions or depassivation such as scratching, abrading, or fretting. Titanium alloys can be classified into three primary groups such as titanium alloys with hexagonal close-packed crystallographic structure; beta titanium alloys with body-centered cubic crystallographic structures; and alpha + beta titanium alloys including near-alpha and near-beta titanium alloys. The article also illustrates the effects of alloying on active anodic corrosion of titanium and repassivation behavior of titanium and titanium-base alloys.

This article discusses factors that influence the effect of alloying, metallurgical treatments, and mechanical treatments on the corrosion resistance of metallic materials, with schematic illustrations.

This article addresses the general effects of the composition, mechanical treatment, surface treatment, and processing on the corrosion resistance of aluminum and aluminum alloys. There are five major alloying elements: copper, manganese, silicon, magnesium, and zinc, which significantly influence the properties of aluminum alloys. There are organic coatings or paints that provide a barrier between a corrosive environment and aluminum surface. Inorganic coatings, including claddings, and enhanced oxides, such as anodized films, Boehmite films, and conversion coatings also help in corrosion prevention. The article assists in the information on selection of fabrication operations, as they play an important role in corrosion resistance.

This article begins with a discussion on the corrosion characteristics of unalloyed magnesium and two major magnesium alloy systems. It shows the effects of iron and 13 other elements on the saltwater corrosion performance of magnesium in binary alloys with increasing levels of the individual elements. The article illustrates the effect of increasing iron, nickel, and copper contamination on the standard ASTM B 117 salt-spray performance of the die-cast AZ91 test specimens as compared to the range of performance observed for cold-rolled steel and die-cast aluminum alloy 380 samples. It discusses the effect of heat treating and cold working on the corrosion rates of the die-cast AZ91 alloy. The article concludes with a description on the causes of corrosion failures in magnesium alloys.

Stainless steels and nickel-base alloys are recognized for their resistance to general corrosion and other categories of corrosion. This article examines the effects of specific alloying elements, metallurgical structure, and mechanical conditioning on corrosion resistance of these materials. It provides information on the compositions of selected stainless steels, copper-nickel, and nickel-base alloys in a tabular form. The article also illustrates the compositional and property linkages for stainless steels and nickel-base alloys.

This article discusses the classification of wear based on the presence or absence of effective lubricants, namely, lubricated and nonlubricated wear. Variations in ambient temperature, atmosphere, load, and sliding speed, as well as variations in material bulk composition, microstructure, surface treatment, and surface finish of steel are also considered. The article discusses the types, wear testing, wear evaluation, and hardness evaluation of abrasive wear. It describes the selection criteria of steels for wear resistance. The article also describes the importance of hardness and microstructure as factors in resistance to wear. It provides a discussion on the resistance of various materials to wear in specific applications. The wear resistance of austenitic manganese steels is also discussed. The article discusses the applications of phosphate coatings, wear-resistant coatings, and ion implantation. It concludes with information on interaction of wear and corrosion.