Ductility and Formability of Metals: A Metallurgical Engineering Perspective uses metallurgical, mechanical and physical principles and concepts to explain ductility while emphasizing the influence of material microstructure on damage mechanisms. Focusing on steel, aluminum, copper, titanium and magnesium alloys, the book examines the strain hardening behaviors of these metals and alloys, the influence of strain rate and temperature, and ductile fracture mechanics. Hot plastic deformation is covered with special consideration given to its interplay with recrystallization phenomena.
Other phenomena such as Dynamic Strain Ageing (DSA) and Adiabatic Shear Banding (ASB) are discussed, and metal working applications such as forging, extrusion and machining are included throughout. Methods for control of ductile cracks in metal parts resulting from rolling, forging, extrusion, drawing, and sheet metal forming are also outlined.
Giovanni Straffelini is professor at the Department of Industrial engineering of the University of Trento
From Chapter 10: Safe plastic forming of metals: general aspects (pagg. 271-272)
Ductility is a special property of metals that allows them to be shaped easily, obtaining products with the required (often complex) geometry. The main plastic shaping processes are:
- Forging
- Rolling
- Extrusion
- Wire drawing
- Sheet metal forming
In every case, a rigid tool plastically deforms a metal workpiece to a certain strain, and at a given temperature and strain rate. The workpiece must have proper ductility to obtain parts free from defects, such as ductile cracks that are the most dangerous defects, or excessive localized (shear) deformation.
Shaping operations also include shearing processes and machining operations by chip removal. In these cases, a low workpiece ductility is taken as an advantage, since ductile fracture favors the process. In this chapter, the general aspects regarding the plastic working processes in safe conditions are outlined, with particular emphasis on the metallurgical characteristics of hot and cold processes. Specific details on the shearing process and machining operations are provided in section 15.2 and chapter 16.
The general concept of formability by plastic deformation (and formability window) is introduced. Metal formability is defined as the ease with which a metal is properly shaped through plastic deformation. It is first linked to ductility, i.e., to the necessity to avoid any crack formation by ductile fracture and also to avoid excessive plastic localization. It is also linked to the flow strenght of metals, i.e., to the necessity of properly carrying out the process with the capability of the available equipement. Hence, to understand the formability of metals and to design a specific process, the knowledge of the plastic behavior of metals must be coupled with a mechanical analysis of the process, aimed at obtaining the strain and stress distributions (and, in some cases, the involved temperature rise).
In the next chapters, the topics will be presented following the same pattern:
- First, the main process methods are introduced;
- Then, a mechanical analysis is outlined for the evaluation of the involved strains, strain rates, and temperature rise;
- At the end, the main types of ductile failures are outlined, with reference to the most important alloys that are used in every specific process.
For the mechanical calculations, different commercial software packages are currently available, with applications of the finite element method (FEM). Howewer, in the next chapters the basic mechanical aspects of the processes are introduced, since this knowledge is pivotal for using such computer programs with the proper awareness and with the capability of introducing any required improvements.
Courtesy by Elsevier.