4. Agree or disagree with the following statements:

1. Magnesium is the lightest structural metal.

2. Magnesium alloys containing big amounts of aluminum, manganese, zinc, etc.

3. Magnesium can't be cast, forged, fabricated, and machined.

4. Magnesium possesses properties that make welding it different than -the welding of steels.

5. The melting point of magnesium isn't close to that of aluminum.

5. Read the text again and make up a plan of this text in a thesis form. Begin with:

• Magnesium is the lightest structural metal.

• Magnesium can be cast, forged and fabricated.

6. Retell the text according to the plan (see ex. 5).

Unit Four

1. Study and try to memorize the following words and word combinations:

1. Etch - кислый раствор

2. to rinse - полоскать, промывать

3.abrasive blasting -абразивная обдувка (обработка пескоструйным аппаратом)

4. impurity - примесь в материале

5. bronze filler metal - медный сплав в качестве присадочного металла

6. dip soldering - низкотемпературная пайка

7. dissimilar materials - разнородные материалы

8. bevel - заострение, конус

9. groove - v-образный

2. Read, translate the text and entitle it

Nickel and the high-nickel alloys are commonly used when corrosion resistance is required. They are used in the chemical industry and the food industry. Nickel and nickel alloys are also widely used as filler metals for joining dissimilar materials and cast iron. When welding, the nickel alloys can be treated much in the same manner as austenitic stainless steels with a few exceptions. These exceptions are:

1. The nickel alloys will acquire a surface oxide coating which melts at a temperature approximately 538°C above the meting point of the base metal.

2. The nickel alloys are susceptible to embitterment at welding temperatures by lead, sulphur, phosphorus, and some low temperature metals and alloys.

3. Weld penetration is less then expected with other metals.

When compensation is made for these three factors the welding procedures used for the nickel alloys can be the same as those used for stainless steel. This is because the melting point, the coefficient of thermal expansion, and the thermal conductivity are similar to austenitic stainless steel.

It is necessary that each of these precautions be considered. The surface oxide should be completely removed from the joint area by grinding, abrasive blasting, machining, or by chemical means. When chemical etches are used they must be completely removed by rinsing prior to welding. The oxide which melts at temperatures above the melting point of the base metal may enter the weld as a foreign material, or impurity, and will greatly reduce the strength and ductility of the weld.

The problem of embitterment at welding temperatures also means that the welding surface must be absolutely clean. Paints, marking crayons, grease, oil, machining lubricants, cutting oils may all contain the ingredients which will cause embitterment. They must be completely removed from the weld area to avoid embitterment. Finally, with respect to the minimum penetration, it is necessary to increase the opening of groove angles and to provide adequate root openings when full-penetration welds are used. The bevel or groove angles should be increased to approximately 40% over those used for carbon. Almost all the welding processes can be used for welding the nickel alloys. In addition, they can be joined by brazing and soldering.