This chapter discusses the basic principles of precipitation hardening, an important strengthening mechanism in nonferrous alloys as well as stainless steel. It begins with a detailed review of the theory of precipitation hardening, then describes its application to aluminum alloys and nickel-base superalloys.

Precipitation hardening is used extensively to strengthen aluminum alloys, magnesium alloys, nickel-base superalloys, beryllium-copper alloys, and precipitation-hardening stainless steels. This chapter discusses two types of particle strengthening: precipitation hardening, which takes place during heat treatment; and true dispersion hardening, which can be achieved by mechanical alloying and powder metallurgy consolidation. It provides information on the three steps of precipitation hardening of aluminum alloys: solution heat treating, rapid quenching, and aging.

The metallurgy of aluminum and its alloys offers a range of opportunities for employing heat treatments to obtain desirable combinations of mechanical and physical properties such that castings meet defined temper requirements. This chapter discusses the processes involved in solution heat treatment, quenching, precipitation hardening, and annealing of aluminum alloys. The effects of these processes on dimensional stability and residual stresses are also discussed. Troubleshooting and diagnosis of heat treating problems are covered in the concluding section of the chapter.

This chapter presents an overview of heat treating of nonferrous alloys. First, a brief discussion on the effects of cold work and annealing on nonferrous alloys is presented. This is followed by a discussion on the mechanisms involved in the more commonly used heat treating procedures for hardening or strengthening, namely solution treating and aging. Examples are presented for heat treating of two commercially important nonferrous alloys, one from the aluminum-copper system and one from the copper-beryllium system.

Porosity in aluminum is caused by the precipitation of hydrogen from liquid solution or by shrinkage during solidification, and more usually by a combination of these effects. Nonmetallic inclusions entrained before solidification influence porosity formation and mechanical properties. This chapter describes the causes and control of porosity and inclusions in aluminum castings as well as the combined effects of hydrogen, shrinkage, and inclusions on the properties of aluminum alloys. In addition, it discusses the applications of radiography to reveal internal discontinuities in aluminum.

This data set presents aging response curves for a wide range of aluminum casting alloys. The aging response curves are of two types: room-temperature, or "natural," curves and artificial, or "high-temperature," curves. The curves in each group are presented in the numeric sequence of the casting alloy designation. The curves included are the results of measurements on individual lots considered representative of the respective alloys and tempers. The properties considered are yield strength, ultimate tensile strength, elongation, and Brinell hardness.

This data set contains approximately 50 growth curves for a wide range of aluminum casting alloys at various temperatures. Growth curves are used to determine the dimensional changes that must be anticipated during service in applications where close dimensional tolerances are required. Hardness curves are provided for many of the alloys. The hardness values are from corresponding aging response studies in which measurements were made on individual lots considered representative of the respective alloys and tempers.

Hot isostatic pressing (HIP) is a process refinement available to address internal porosity in castings. The HIP process may be used, in particular, for applications requiring very high quality and performance. This chapter discusses the principles, advantages, and disadvantages of HIP. It describes the effect of HIP on tensile properties and on the fatigue performance of aluminum alloy castings. In addition, the chapter discusses the processes involved in radiographic inspection of HIP-processed castings.

Aluminum casting alloy compositions parallel those of wrought alloys in many respects. However, because work hardening plays no significant role in the development of casting properties, the use and purposes of some alloying elements differ in casting alloys versus wrought alloys. This chapter provides information on specifications and widely used designation systems and alloy nomenclature for aluminum casting alloys. It describes the composition of seven basic families of aluminum casting alloys: aluminum-copper, aluminum-silicon-copper, aluminum-silicon, aluminum-silicon-magnesium, aluminum-magnesium, aluminum-zinc-magnesium, and aluminum-tin. The chapter discusses the effects of alloying elements on the properties of cast aluminum. It provides information on various alloys that are grouped with respect to their applications or major performance characteristics.

This chapter first introduces the various factors that may alter the physical and mechanical properties of aluminum castings that are addressed in the other chapters in the book. Then, it presents the historical development of aluminum castings, followed by a discussion on the advantages and limitations of aluminum castings. Next, the chapter describes the major trends that are influencing the increased use of aluminum castings. Finally, it introduces the considerations involved in the selection of an appropriate aluminum alloy and casting process for a given application.

The stress-strain curves in this data set are representative examples of the behavior of several cast alloys under tensile or compressive loads. The curves are arranged by alloy designation. Each figure cites the original source of the curve and provides pertinent background information as available. Compressive tangent modulus curves are presented for certain alloys. The effects of cyclic loading are given on several curves.

In castings, microstructural features are products of metal chemistry and solidification conditions. The microstructural features, excluding defects, that most strongly affect the mechanical properties or aluminum castings are size, form, and distribution of intermetallic phases; dendrite arm spacing; grain size and shape; and eutectic modification and primary phase refinement. This chapter discusses the effects of these microstructural features on properties and methods for controlling them. The chapter concludes with a detailed examination of the refinement of hypereutectic aluminum-silicon alloys.

This chapter reviews and provides data tables for the wide range of properties and performance characteristics that are possible with specific aluminum casting alloys and tempers. Properties and performance attributes addressed include casting and finishing characteristics; typical physical properties; typical and minimum (design) mechanical properties; fatigue strength; fracture resistance, including subcritical crack growth; and resistance to general corrosion and to stress-corrosion cracking. The chapter concludes with information on the properties of cast aluminum matrix composites.

This chapter begins with information on the historical development of aluminum alloy castings. It then covers the basic factors involved in the selection of a casting process. This is followed by sections describing the various categories of casting processes and their variants: expendable mold gravity-feed casting, nonexpendable (permanent) mold gravity feed casting, and pressure die casting. Next, the chapter describes the technologies used to produce premium engineered castings and when such castings may be relevant. The chapter concludes with descriptions of other process technologies used with castings, including metallurgical bonding, metal-matrix composites, and hot isostatic pressing.

Grain size has a determining effect on the mechanical properties of steel and responds favorably to forging and heat treating. This chapter explains how to measure and quantify grain size and how to control it through thermal cycling and forging operations. It describes how surface tension acting on grain-boundary segments contributes to grain growth and how the formation of new grains, driven by phase transformations and recrystallization, lead to a reduction in average grain size. It also discusses the effect of alloying elements on grain growth rates, particularly the curbing effect of particle and solute drag.

The term heat treatable alloys is used in reference to alloys that can be hardened by heat treatment, and this chapter briefly describes the major types of heat treatable nonferrous alloys. The discussion provides a general description of annealing cold-worked metals and describes some of the common nonferrous alloys that can be hardened through heat treatment. The nonferrous alloys covered include aluminum alloys, cobalt alloys, copper alloys, magnesium alloys, nickel alloys, and titanium alloys.

Nonferrous alloys are heat treated for a variety of reasons. Heat treating can reduce internal stresses, redistribute alloying elements, promote grain formation and growth, produce new phases, and alter surface chemistry. This chapter describes heat treatment processes and how nonferrous alloys respond to them. It provides information on aluminum, cobalt, copper, magnesium, nickel, and titanium alloys and their composition, microstructure, properties, and processing characteristics.

This chapter is a collection of tables listing: cast alloy designations of Aluminum Association, along with their general applications; the chemical compositions of the frequently used alloys for gravity permanent molds, low-pressure permanent molds, squeeze castings, and die castings; the typical tensile properties of die cast alloys; and the designations of different heat treatments and their description. The tables also list the temperatures and times of typical heat treatment cycles for different permanent mold cast alloys; typical components in sand, gravity, and low-pressure permanent mold castings and die castings, the functional requirements of each process, and the corresponding suitable alloys and heat treatments; and alloys that are high vacuum die cast for structural castings. The chapter also presents examples of photomicrographs of some alloys cast by different processes.

This chapter discusses the processes used in manufacturing to thermally alter the properties of metals and alloys. It begins with a review of the iron-carbon system, the factors that affect hardenability, and the use of continuous cooling transformation diagrams. It then explains how various steels respond to heat treatments, such as annealing, normalizing, spheroidizing, tempering, and direct and interrupted quenching, and surface-hardening processes, such as flame and induction hardening, carburizing, nitriding, and carbonitriding. It also addresses the issue of temper embrittlement and discusses the effect of precipitation hardening on aluminum and other alloys.