A metal material is a general designation of a material consisting of a metal element or a metal element. Including pure metals, alloys, metal materials, metal compounds and special metal materials, etc.. Note: metal oxides (e.g., aluminium oxide) do not belong to metallic materials.
The development of human civilization and the progress of the society are closely related to the metal materials. After the stone age appears after the bronze age and the iron age, all with the application of metal material is marked by its age. Modern, wide variety of metal materials has become an important material foundation for the development of human society.
Metal materials are usually divided into ferrous metals, non-ferrous metals and special metal materials.
(1) black metal, also known as iron and steel materials, including containing iron more than 90% of industrial pure iron, carbon 2% ~ 4% of cast iron containing, containing less than 2% of the carbon steel, and various uses of structural steel, stainless steel, heat-resistant steel, high temperature alloy, stainless steel, precision alloy. The generalized black metal also includes chromium, manganese and its alloys.
(2) non-ferrous metals are all metals except iron, chromium and manganese, which are usually classified as light metals, heavy metals, precious metals, semi metals, rare metals and rare earth metals. The strength and hardness of non-ferrous alloys are generally higher than those of pure metals, and the resistance is large and the temperature coefficient of resistance is small.
(3) special metal materials, including structural and functional metallic materials for different purposes. There are obtained by rapid solidification process of amorphous metal material, as well as quasicrystal, microcrystalline and nanocrystalline metal materials; and stealth, anti hydrogen, superconductivity, shape memory, wear resistance, vibration damping special alloys and metal matrix composites.
Generally divided into two types of process performance and performance. The so-called process performance refers to the performance of mechanical parts in the process of manufacturing, metal materials in the set of cold and hot processing conditions. The process performance of the metal material is good or bad, which determines its ability to adapt to the forming process in the manufacturing process. Due to the different processing conditions, the requirements of the process performance is also different, such as casting properties, can be welding, forging, heat treatment, machining, etc..
The so-called performance is the use of mechanical parts in the use of the conditions, the performance of metal materials, including mechanical properties, physical properties, chemical properties, etc.. The use of metal materials is good or bad, which determines its scope of use and service life. In the mechanical manufacturing industry, the general mechanical parts are used in normal temperature, normal pressure and very strong corrosive medium, and in the use of mechanical parts in the process will bear the role of different loads.
The performance of a metal material under the action of a load, known as mechanical properties (in the past, also known as mechanical properties). The mechanical properties of metal materials are the main basis for the design and material selection of the parts. The mechanical properties of metallic materials are different, such as tensile, compression, torsion, impact, cyclic loading, and so on. Mechanical properties, such as strength, plasticity, hardness, impact toughness, repeated impact resistance and fatigue limit, etc..
 characteristics of metal materials
Many mechanical parts and engineering components are subjected to alternating load operation. Under the action of alternating load, although should stress level is less than the material yield limit, but after a long time of stress after repeated cycles, sudden brittle fracture, this phenomenon called the fatigue of metal material. The characteristics of fatigue fracture of metal materials is: (1) the load stress is alternating; (2) the load effect time is longer; (3) the fault is instantaneous; and (4) whether it is plastic material or brittle materials, in fatigue and fracture zone is brittle. Therefore, fatigue fracture is the most common and most dangerous type of fracture in engineering.
The fatigue phenomena of metal materials can be divided into the following according to the different conditions:
(1) high cycle fatigue: the number of stress cycles at 100000 or more under low stress (working stress is lower than the yield limit of the material, even below the elastic limit). It is one of the most common fatigue damage. High cycle fatigue is generally referred to as fatigue.
(2) low cycle fatigue: the number of stress cycles under 10000~100000 in the case of high stress (stress close to the yield limit of the material) or high strain condition. Because the alternating plastic strain plays a major role in this kind of fatigue failure, it is also called plastic fatigue or strain fatigue.
(3) thermal fatigue: the fatigue failure caused by the thermal stress caused by temperature changes.
(4) corrosion fatigue: the machine parts in alternating load and corrosive medium (such as acid, alkali, water, active gas, etc.)
Under the common action, the fatigue damage.
(5) contact fatigue: This is refers to the contact surface of machine parts and subjected to repeated in contact stress, pock exfoliation or crushing surface spalling, thus resulting in mechanical failure.
Plasticity refers to the ability to produce permanent deformation (plastic deformation) without damage under the action of external force. Metallic materials when subjected to tension, length and cross-sectional area to change. Therefore, metal plastic can length elongation and cross-section contraction (section shrinkage) two indicators to measure.
Metal material elongation and section shrinkage rate is bigger, said the material of the plastic is better, that is, the material can bear larger plastic deformation without failure. Generally the extension rate is greater than