Unit 9. Metals and their alloys.

Task for selfstudy:

- read the texts

- write down all special terms to each of the texts

- answer the questions

- make a report on any metal you like

ALLOYS

Pure metals are comparatively seldom used; in engi­neering, application is made chiefly of alloys which consist of two or more metals, or of metals and metal­loids.

Alloys are metallic solids, complex in composition,
formed as a result of the freezing of the melt — the liquid
solution of two or more metals, or metals and metalloids.

Each constituent of an alloy is called a component. Alloys may be binary (two-component), ternary (three-component), etc.

The ability of various metals to form alloys differs greatly and, therefore, the structure of various alloys after solidification may also be very diverse.

In the liquid state, alloys are entirely homogeneous and from the physical point of view constitute a single phase. Nonhomogeneity may appear when an alloy is transformed from the liquid to the solid state, i.e. several solid phases are formed. After solidification, alloys may consist of one, two or more phases depending upon the nature of their components. Certain metals are not mutually soluble in the liquid stale; they form two layers with different specific weights (e.g., lead and iron, lead and zinc, etc.). It is difficult to form an alloy in such cases since it is necessary to mix the metals into each other.

       ALUMINIUM AND ITS ALLOYS

Next to oxygen, aluminium is the most abundant element in nature: about 7.45 per cent of the earth's crust consists of aluminium.

Aluminium is extracted from rock with a high alumina content. The most important sources are bauxite, kaolin, nepheline and alunile.

Bauxite is the principal source of aluminium. The less silica in a bauxite the higher its quality as an aluminium ore. Kaolin clays are very abundant in nature but the extraction of aluminium from these ores presents diffi­culties due to the considerable amount of silica present.

The most important properties of aluminium are its low specific gravity (2.7), high electrical and thermal conductivities, high ductility, and corrosion resistance in various media.

Pure aluminium has only few applications; it is used for the manufacture of electrical wire, chemical apparatus, household utensils and for coating other metals.

Aluminium alloys are more widely used in industry. Wrought aluminium alloys have a high mechanical strength which in some cases approaches the strength of steel. Wrought aluminium alloys are further classified as non-heat-treatable and heat-treatable alloys. .Wrought aluminium alloys also include complex alloys of aluminium with copper, nickel, iron, silicon and other alloying elements. Complex wrought aluminium alloys of the duralumin (dural) type and certain others have found most extensive application in many industries.

Several grades of duralumin are available in the Russia. They are identified by the Russian letter Д fol­lowed by a figure indicating the number of the alloy in the series. Duralumin, grade Д-1 can be obtained in the form of sheets, bar stock and tubing; grades Д-6 and Д-16 аre usually produced in the form of bars, and grade Д-ЗП is made as wire for rivets.

Answer the following questions:

1. What elements are the most abundant in nature?

2. What are the most important sources of alu­minium?

3. What are the most important properties of alu­minium?

4. Is pure aluminium widely used?

5. Do wrought aluminium alloys have a high me­chanical strength?

6. How are wrought aluminium alloys further classified?

7. What complex alloys do wrought aluminium alloys also include?

8. What aluminium alloys have found most extensiveapplication in many industries?

9. How are various grades of duralumin identified?

MAGNESIUM AND ITS ALLOYS

Magnesium has a specific gravity of approximately 1.7; its alloys are the lightest of all engineering metals employed.

The melting point of magnesium is 650° C; its boiling point is 1007° C. Magnesium is very inflammable and burns with a dazzlingflame, developing a great deal of heat.

The mechanical properties of magnesium, especially the tensile strength, are very low and therefore pure magnesium is not employed in engineering.

The alloys of magnesium possess much better mechan­ical properties which ensure their wide application.

The principal alloying elements in magnesium alloys are aluminium, zinc and manganese. Aluminium, added in amounts up to 11 per cent, increases the hardness, tensile strength and fluidity of the alloy. Up to 2 per cent zinc is added to improve the ductility (relative elongation) and castability. The addition of 0.1-0.5 per cent manga­nese raises the corrosion resistance of magnesium alloys.

Small additions of cerium, zirconium and beryllium enable a fine-grained structure to be obtained, they also increase the ductility and oxidation resistance of the alloys at elevated temperatures.

Magnesium alloys are classified into two groups: wrought alloys, grades MA1, MA2, casting alloys, grades MЛ4, MЛ5.

Wrought magnesium alloys MA1 and MA2 are chiefly used for hot smith and closed-die forged machine pants. They are less frequently used as sheets, tubing or bar stock.

Magnesium casting alloys MЛ4 and MЛ5 are widely used as foundry material though their castability is inferior to that of aluminium-base alloys.

Answer the following questions:

1. What specific gravity has magnesium?

2. What is the melting point of magnesium?

3. Why is pure magnesium not employed in engineering?

4. What are the principal alloying elements in magnesium alloys?

5. How much aluminium is added to magnesium?

6. How much zinc is added to magnesium?

7.How much manganese is added to magnesium?                                     8. For what purpose are small additions of cerium, zirconium and beryllium added to magnesium?

COPPER AND ITS ALLOYS

Copper is a valuable metal. Its wide application in many fields of engineering is due to its exceptionally high electrical and thermal conductivity, low oxidisability, good ductility and to the fact that it is the basis of the important industrial alloys, brass and bronze.

The raw materials for the production of copper are sulphide or oxide copper ores. Most of the copper is smelted from sulphide ores (about 80 per cent) while oxide ores account for only 15 to 20 per cent. Sulphide ores are more wide-spread in nature due to the higher affinity of copper for sulphur than for oxygen.

  The most abundant copper sulphide ore is copper pyrite containing the mineral chalcopyrite (Cu₂Fe₂S₄). In some cases, the so-called copper glance is used; it contains the mineral chalcocite (Cu₂S). All copper ores are very lean as they contain only from 1 to 5% Cu. Therefore, before smelting they must be concentrated by flotation. Flotation converts lean copper sulphide ores into a con­centrate containing from 15 to 20% Cu.

Before smelting, the copper concentrate and rich copper sulphide ores are subjected to an oxidising roasting process at 600—900° C thereby part of the sulphur is removed in the form of a gas. This gas is trapped and utilised in the production of sulphuric acid.

Various grades of copper are used for engineering purposes. It must be noted that even a minute amount of impurities sharply alters the properties of pure copper.

The mechanical strength of pure copper is not high and depends upon the degree of deformation (reduction in working). Pure copper is used chiefly for electrical engi­neering products such as cables, busbars and wire.

The copper alloys are more widely employed. The alloying of copper with other elements increases the strength of the metal in some cases and improves the anticorrosive and antifriction properties in others. Copper alloys comprise two main groups — brasses and bronzes. Alloys of copper and zinc are called brasses. The addition of appreciable amount of tin, nickel, manganese, alumin­ium and other elements to copper-zinc alloys imparts higher hardness, strength and other desirable qualities. Complex copper-zinc alloys comprising three, four or more components are special brasses.

In Russia brasses are identified by means of the Russian letter Л (the first of the Russian word for brass) followed by letters designating the chief elements and numbers which indicate percentage content of these elements. Thus, grade ЛT 96 is the brass tombac (T) containing 96% Cu and Zn. The designation of gradе ЛЖМЦ-59-l-l indicates that the brass contains 59% Cu, 1 % Fe, 1 % Mn, the remainder is Zn.

Alloys of copper with a number of elements including tin, aluminium, silicon, manganese, iron and beryllium are called bronzes. Tin bronzes are divided into two groups: wrought bronzes, containing up to 6% Sn, and casting bronzes, containing over 6% Sn. Special bronzd are copper-base alloys in which the principal admixtures are Al, Ni, Mn, Si, Fe, Be and others. Special bronzes are fully equivalent substitutes for the more expensive tin bronzes and, therefore, have great economical value. These bronzes are designated on the same principle as brasses. The designation begins with the Russian letters Бp (the first two letters of the Russian for bronze) which are followed by letters indicating the main elements and numbers showing the average percentage of these elements.

Certain grades of special bronzes deserve more detailed consideration. Aluminium bronzes contain from 4 to 11% Al; their high mechanical properties and corrosion resistance considerably surpass those of tin bronzes and brasses. The castability of aluminium bronzes is good and the are frequently used in foundry practice. Sheets, strips, bars and wire are made of grades БpA5 and БpA4 by the rolling process. Aluminiur bronzes with admixtures of iron and manganese, grades БpAЖ9-4, БpAЖMЦ10-3-1.5 and БpAMЦ9-2, are suitable for castings and for working, especially for smith and closed-die forging.

Answer the following questions:

1. What are the raw materials for the production of copper?

2. Why must all copper ores be concentrated by flotation?

3. Whаt purpose is pure copper chiefly used for?

4. What properties does the alloying of copper with other elements increase?

5. What main groups do copper alloys comprise?

6. What alloys of copper are called bronzes?

7. Into what groups are bronzes divided?

8. Why are aluminium bronzes frequently used  in foundry practice?

TITANIUM AND ITS ALLOYS

As an engineering material titanium has been widely applied only in the last years.

Titanium is a silvery-white metal which melts at approximately 1668°C and has a specific gravity of 4.505. Commercially pure titanium possesses high strength prop­erties. The tensile strength of most titanium alloys ranges from 100 to 140 kg/mm², in conjunction with high elongation.

The hardness, tensile strength and yield point of tita­nium are increased with the degree of cold deformation. The elongation value drops rapidly when the degree of cold deformation (reduction) exceeds 50 per cent and becomes equal to 10 per cent. Impurities found in com­mercial titanium can be divided into two groups: elements which form interstitial solid solutions with titanium (O₂, N, C and H₂) and elements which form substitution solid solutions (Fe and other metallic elements). The first have a much greater effect on the mechanical properties than those in the second group.

Even very small amounts of oxygen and nitrogen in titanium alloys sharply reduce the ductility. A carbon content of more than 0.2 per cent reduces both the ductility and impact strength of a titanium alloy. It is supposed that the brittleness of titanium is a result of strain ageing and is connected with the presence of dissolved hydrogen in the beta-phase.

Titanium and its alloys are hardened either by a sur­face heat treatment followed by ageing at 400°—500° C or by producing a case which contains nitrogen, carbon and boron Industrial titanium alloys contain vanadium, molybdenum, chromium, manganese, aluminium, tin, iron or other elements, singly or in various combinations.

A combination of high mechanical properties with low specific weight and excellent corrosion resistance enables titanium to be used in building supersonic air craft.

Answer the following questions:

1. What is titanium?

2. What does the hardness, tensile strength and yield point of titanium depend upon?

3. Do very small amounts of oxygen and nitrogen in titanium alloys reduce the ductility?

4. How are titanium and its alloys hardened?

5. What constituents  do industrial titanium alloys contain?

Литература

1. Алехина М.С. Английский для металлургов. М.: Русский язык, 2005.

2. Андреев Г.Я., Гураль Л.Л., Лев А.Л. Сборник технических текстов на английском языке. М.: Издательство «Высшая школа», 1972.

3. Иллюстрированный словарь английского и русского языка с указателями. М.: Живой язык, 2003.

4. Парахина А.В. Пособие по переводу технических текстов с английского языка на русский. М.: Издательство «Высшая школа», 1972.

Contents (Содержание)

Пояснительная записка…………………………………………………………...3

Unit 1. Metallurgy

(Глава 1. Металлургия)…………………………………………………………….4 Unit 2. Physical properties of metals and alloys

(Глава 2. Физические свойства металлов и сплавов)…………………………5

Unit 3. Mechanical properties of metals and alloys

(Глава 3. Механические свойства металлов и сплавов)……………………...8

Unit 4. Foundry equipment.

(Глава 4. Оборудование литейного завода)……………………………………10 Unit 5. Sand molding equipment and materials

(Глава 5. оборудование и материалы для литейных форм из песка)……….13

Unit 6. Types of molding machines

(Глава 6. Типы машин для создания литейных форм)………………………15

Unit 7. Casting metals

(Глава 7. Литье металлов)……………………………………………………….17

Unit 8. Types of furnaces.

(Глава 8. Типы печей)…………………………………………………………...18

Unit 9. Metals and their alloys.

(Глава 9. Металлы и их сплавы)………………………………………………...24

Литература……………………………………………………………………….29