Page 179 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Chapter 6 Nonferrous Metals and Alloys: Production, General Properties, and Applications

alloys that were standardized respectively). Specific information related to this
standardized alloy can then be obtained.
° T6 indicates that this alloy has been solution treated and artificially aged.

Production. Magnesium is the third-most-abundant metallic element (2%) in the
earth’s crust, after iron and aluminum. Most magnesium comes from seawater, which
contains 0.13% magnesium in the form of magnesium chloride. First produced in
1808, magnesium metal can be obtained electrolytically or by thermal reduction. In
the electrolytic inet/ood, seawater is mixed with lime (calcium hydroxide) in settling
tanks. Magnesium hydroxide precipitates to the bottom, is filtered and mixed with
hydrochloric acid. The resulting solution is subjected to electrolysis (as is done with
aluminum), producing magnesium metal, which is then cast into ingots for further
processing into various shapes. In the thermal-reduction met/ood, magnesium ores
(dolomite, magnesite, and other rocks) are broken down with reducing agents (such
as powdered ferrosilicon, an alloy of iron and silicon) by heating the mixture in a
vacuum chamber. As a result of this reaction, vapors of magnesium form, and they
condense into magnesium crystals, which are then melted, refined, and poured into
ingots to be processed further into various shapes.

6.4 Copper and Copper Alloys

First produced in about 4000 B.C., copper (Cu, from the Latin cuprurn) and its alloys
have properties somewhat similar to those of aluminum and its alloys. In addition,
they are among the best conductors of electricity and heat (Tables 3.1 and 3.2), and
they have good corrosion resistance. Copper and its alloys can be processed easily by
various forming, machining, casting, and joining techniques.
Copper alloys often are attractive for applications in which a combination of
electrical, mechanical, nonmagnetic, corrosion-resistant, thermally conductive, and
wear-resistant qualities are required. Applications include electrical and electronic
components, springs, coins, plumbing components, heat exchangers, marine hard-
ware, and consumer goods (such as cooking utensils, jewelry, and other decorative
objects). Although aluminum is the most common material for dies in polymer
injection molding (Section 19.3), copper often is used because of its better thermal
properties. Pure copper also can be used as a solid lubricant in hot-metal-forming
operations.
Copper alloys can acquire a wide variety of properties by the addition of alloy-
ing elements and by heat treatment, to improve their manufacturing characteristics.
The most common copper alloys are brasses and bronzes. Brass (an alloy of copper
and zinc) is one of the earliest alloys developed and has numerous applications, in-
cluding decorative objects (Table 6.6). Bronze is an alloy of copper and tin (Table 6.7).
There are also other bronzes, such as aluminum bronze (an alloy of copper and
aluminum) and tin bronzes. Beryllium copper (or beryllium bronze) and phosphor
bronze have good strength and hardness for applications such as springs and bearings.
Other major copper alloys are copper nickels and nickel sili/ers.

Designation of Copper Alloys. In the Unified Numbering System, copper is iden-
tified with the letter C, such as C26200 for cartridge brass. In addition to being
identified by their composition, copper and copper alloys are known by various
names (Tables 6.6 and 6.7). The temper designations (such as 1/Z hard, extra
hard, extra spring, and so on) are based on degree of cold work (such as by rolling
or drawing).