Wrought aluminium alloys

For many purposes, castings are not suitable and worked or wrought articles are required. In general, their production starts with a casting operation in which an ingot of suitable size and shape is formed. This ingot is then rolled, pressed, extruded, or otherwise deformed by the application of severe mechanical stresses so as to produce the article desired.

Of all the working processes, hammer forging is the simplest in its essence and probably was the first to develop in the history of metal working. In connection with aluminium, however, it was one of the later developments. One of the difficulties to be overcome is that the temperature range over which aluminium can be forged satisfactorily is rather narrow, particularly for the strong alloys. Also, at their forging temperature these alloys are much stronger than steel is at its forging temperature, so that the size of hammer and the power required to forge a connecting rod (for example) out of aluminium are greater than that required to forge the same article out of steel.

Any mechanical working, such as rolling, breaks down the cast structure of the original ingot and tends to produce a fibrous structure, which very much improves the physical properties of the article. Working under a hammer - the simplest method of forging - may sometimes be advantageously replaced by a press-forging operation in which the lump of metal, preferably previously broken down by rolling, is formed into the desired shape while hot, by successive strokes of a press provided with suitable dies. In any forging operation, care must be taken to control and direct the flow of the metal during the working operation, so that the direction of the resulting "fiber" gives the results desired in the finished article. The dominant characteristic of the forging process, as compared with any casting process for producing the same article, is the marked metallurgical superiority of the product. Not only are the mechanical properties higher but forgings are also inherently much freer of hidden defects, such as dross or porosity, and at the same time have nearly the dimensional accuracy of permanent-mould castings.

A special kind of permanent mould casting process is spoken of as "die casting", or sometimes "pressure die casting". In this, the water-cooled steel mould or "die" is mounted adjacent to a crucible of molten metal, and by an ingenious device successive "shots" of molten metal are squirted into the die, so that the die is filled at each "shot" with the molten metal under pressure. In the subsequently developed "cold-chamber" process, the charge of molten metal is cooled to partial solidification and then forced into the die by heavy hydraulic pressure. By both processes, it is possible to fill the die in a fraction of a second. Consequently, castings with extremely thin walls can be made, with the assurance that the metal will not freeze before the narrow-cavities of the mould have been properly filled.

The oldest of the wrought aluminium alloys now in production is the one called 3S, which contains about 1.25 % of manganese added to commercial aluminium. The addition of this small amount of manganese increases the tensile strength of the sheet or other wrought article by about one third without very seriously reducing its elongation. Moreover, manganese is one of the few elements that can be added to aluminium without decreasing its corrosion resistance. This alloy is said to have been developed under stress in the early days to meet a very serious condition threatening the loss of a large amount of business because of the inferior corrosion resistance of the binary copper-alloy sheet that was then being produced, and it was extensively made and sold for many years before it was introduced abroad. Its most common use is in cooking utensils, where it increases the hardness and strength of the utensil without increasing its weight, and without unduly increasing its fabrication cost.

Attempts to add copper and zinc in alloys for the production of sheet were at first unsuccessful because of the poor corrosion resistance of such sheet. It was only after the introduction of the heat treatment of copper alloys that their corrosion resistance became satisfactory. Early attempts to produce aluminium-magnesium alloys, on the other hand, failed because of rolling difficulties. The alloys themselves had excellent properties but their economical fabrication was beyond the skill of the industry at that time. As the result of intensive study and improvements in fabricating technique, these alloys are now coming into their own, and are among our most corrosion-resistant aluminium alloys.

Task 1

Find in the text English equivalents to the following words:

виливки, злитки підходящих розмірів та форм, прокатувати, механічні навантаження, видавлювати (пресувати), кування молотом, температурний діапазон, переборювати, згар, лита структура, прес-форма (кокіль), готовий виріб, скриті дефекти, окалина, оригінальний пристрій, наповнювати, промисловий алюміній, межа міцності, вартість виробництва, вприскувати метал, технологія виробництва.

Task 2

Match the following words with their translation:

1. crucible	a) порожнина
2. fiber	b) шихта, завантаження
3. cavity	c) лист
4. hammer	d) камера
5. charge	e) удар
6. ingot	f) тигель
7. article	g) молот
8. chamber	h) виріб
9. sheet	i) волокно
10. stroke	j) злиток
Task 3	Fill in the correct words from the list below. Use each word only once. Translate the word combinations into Ukrainian.

fabricating, device, amount, size, dimensional, stress, mold,

corrosion, properly, metallurgical, second, water-cooled

1. … accuracy	7. permanent … castings
2. suitable … and shape	8. … filled
3. mechanical …	9. small … of manganese
4. marked … superiority	10. … steel mold
5. fraction of a …	11. poor … resistance
6. … technique	12. ingenious …

Task 4

Give Ukrainian equivalents to the following words and word combinations:

castings, wrought alloy, ingot of suitable size and shape, to roll, to press, to extrude, hammer forging, metal working, to overcome, temperature range, connecting rod, to break down, cast structure, fibrous, to improve the physical properties, the simplest method of forging, press-forging operation, the lump of metal, successive strokes, dies, finished article, dominant characteristic, hidden defects, dross, porosity, "die casting", water-cooled mould, to be mounted, ingenious device, to squirt, to fill, cold-chamber process, partial solidification, hydraulic pressure, commercial aluminium, tensile strength, elongation, corrosion resistance, inferior, binary copper-alloy, hardness, weight, fabrication cost, to add, heat treatment, to fail, fabricating technique.

Task 5

Make up the word combinations from the words in columns A and B. Translate them into Ukrainian paying attention to the Past Participle in the function of attribute.

A	B
1. worked	a. metal
2. required	b. article
3. previously broken down	c. defects
4. desired	d. mould
5. finished	e. power
6. marked	f. shape
7. water-cooled	g. manganese
8. added	h. results
9. molten	i. superiority
10. hidden	j. elements

Task 6

Make up the sentences from the given words. Start with the underlined word.

1. forging, working, the history, The hammer, is, working, in, process, metal, of, the simplest.

2. defects, Forgings, freer, mechanical, higher, and, properties, much, hidden, have, of, are.

3. the addition, The tensile, of, small, be, of, manganese, the, can, increased, strength, by, amount, article, of.

Task 7

Fill in the gaps with given words and word combinations according to the meaning:

hidden defects, a press-forging operation, resistance

hammer, the tensile strength, metallurgical superiority

1. _____ forging probably was the first to develop in the history of metal working and one of the later developments.

2. Working under a hammer may sometimes be replaced by _____ in which the piece of metal is formed into the desired shape while hot by successive strokes of a press provided with suitable dies.

3. The dominant characteristic of the forging process is the marked _____ of the product.

4. Forgings are also much freer of _____, such as dross or porosity, and have nearly the dimensional accuracy of permanent-mold castings.

5. The addition of this small amount of manganese increases _____ of the sheet or other wrought article by about one third without very seriously reducing its elongation.

6. Manganese is one of the few elements that can be added to aluminium without decreasing its corrosion _____.

Task 8

Answer the following questions:

1. Why are the working processes used?

2. What types of working processes are mentioned in the text?

3. How can any mechanical working influence the physical properties of the article?

4. What care must be taken in any forging operation?

5. What is the dominant characteristic of the forging process?

6. What aluminium alloys are mentioned in the text?

7. Give the title to each paragraph.

Task 9

Read and dramatize the following dialogue.

A: What do you know about hammer forging?

B: Well, it is the simplest working process in the history of metal working.

A: And what about aluminium? Can it be forged satisfactorily?

B: Yes, it can, but the temperature range over which it can be forged satisfactorily is rather narrow, particularly for the strong alloys.

A: Aluminium alloys are known to be much stronger than steel at their forging temperatures, so the size of hammer must be greater than that required to forge the same article of steel.

B: And the power required must be greater as well.

Task 10

Make up your own dialogues about 1) press-forging operation, 2) die casting, 3) cold chamber process using the information from the text. The dialogue above can be used as a model.

Дата добавления: 2015-07-20