Magnesium is a highly versatile metal which is non-toxic, has excellent machining qualities, and exhibits a capacity to dampen and absorb vibration and electromagnetic waves. The commercial possibilities of the electrolytic method of production were first exploited in 1909 by a German company. In the 1990's Europe went through a change in its laws regarding reducing the greenhouse effect. One effective way in achieving this goal is reducing the weight of vehicles. It is coming the golden age for magnesium. Many people enjoy lighter accessories such as canes and wheel chairs. Others enjoy lighter leisure equipment such as backpacks, suitcases and lighter tennis rackets.
Magnesium and magnesium alloys are nonferrous metals with low density, good ductility, moderate strength and good corrosion resistance. When used an alloying agent, they can improve the mechanical, fabrication, and welding characteristics of aluminum. Some magnesium and magnesium alloys are used as lightweight materials in vehicles such as cars and trucks. These magnesium alloys have a relatively low density and can help improve fuel efficiency. Magnesium-base alloys are also used in airplanes and aerospace applications because of their relatively low density compared to aluminum. Magnesium can also be alloyed with lead, zinc and other nonferrous composites. A magnesium alloy can include yttrium to provide increased strength.
We can arrange some major magnesium alloys:
- RZ5 - magnesium-casting alloy that contains zinc, rare earth metals, and zirconium. Used for helicopter gearboxes, video cameras, high-performance vehicles, computer parts, and military equipment.
- WE43 is a high-strength, isotropic, magnesium-based alloy that is valued for its long-term stability at high temperatures. The industry uses it in aircraft, aerospace engines and high-performance vehicles.
- MSR is the most common type of magnesium and magnesium alloys. MSR is fully heat-treatable and contains silver and rare earth metals.
- EQ21 contains silver and rare earth metals, but has less silver than MSR. EQ21 alloys retain their properties at elevated temperatures and are suitable for aerospace, automotive, and military applications.
Magnesium alloys have line of properties. We can find it in all common forms in which metals are commercially used. Practically pure magnesium, 99.8 per cent is supplied as powder, ribbon, wire, and extruded and rolled strip. Alloys can be present in various forms like casting, sheet and plate, shapes and others. Magnesium alloys are especially workable by hot forming methods. Structures in the alloys are readily assembled by welding and by riveting. Parts in the alloys can be machined at higher speeds and at lower costs than in most other common metals.
Cast magnesium alloys are supplied with tensile strengths up to about 40,000 pounds per square inch (~280 M Pa) and yield strengths up to about 23,000 pounds (~160 M Pa). Wrought magnesium alloys are produced with tensile strengths up to about 52,000 (~360 M Pa) pounds and yield strengths up to about 44,000 pounds (~300 M Pa). Different combinations of mechanical properties may be obtained by suitable heat treatment of some compositions. When we talking about the modulus of elasticity of magnesium alloys may be taken as 6.5 million pounds per square inch (45 G Pa) and the modulus of rigidity as 2.4 million pounds (16 G Pa).
Magnesium alloy can be described with yield strength, tensile strength and hardness. In general, the strength, hardness, and endurance limit of magnesium alloys are substantially impaired at 300°F (150°C). However, some compositions have been developed especially for service at temperatures above 500°F (260°C).
Some outstanding physical properties of magnesium are relatively high coefficient of thermal expansion, thermal conductivity, also low electrical conductivity and specific heat.
In the same case like aluminum production, magnesium alloys rather than steel savings may be affected. The volume of metal in a part may be substantially the same irrespective of the material used, however when comparing metal costs, the price per pound of magnesium should be divided by the ratio of the specific gravities involved.
The economy arising in machining magnesium alloys may onset an disadvantageous price relation with a material which costs less on a volume basis but is difficult to machine. Also, the fact that a die-casting may be made of a magnesium-base composition and used in place of another material which is not suitable for the die-casting process may lead to real savings.
Pure magnesium materials are supplied in various compositions including the commercially pure metal (99.8 per cent minimum), alloys for casting, and alloys for the manufacture of wrought products. Varied mixtures are used for casting as contrasted with those for rolling, forging, or other working. That kind of magnesium can't find practical application in engineering design.
All pure magnesium has many important nonstructural uses like these in pyrotechnics. According to alloyed magnesium provides material with a wide range of mechanical properties and nonferrous metallurgy.
Mainly magnesium alloys are used like casting alloys usually contain varied percentages of calcium, aluminum, manganese and zinc. Usually calcium is added in small amount - about 0.10 % to some alloys. Aluminum is the dominant element in magnesium alloys - nearly 10 %. New alloys developed during late years contain rare-earth metals and zirconium. These provide increased resistance to creep and stress-rupture at elevated temperatures. Almost all of the casting alloys may be heat treated to improve the mechanical properties, a notable exception being alloy M1A.
Wrought magnesium alloys are generally used for the manufacture of wrought products like bars, rods, solid shapes, hollow shapes, and tubing. The commercially available production of magnesium alloys includes also flat rolled products, forgings and impact extrusions. Magnesium alloys for wrought products are classified as non-heat treatable and heat treatable. Maximum mechanical properties in a typical alloy are developed in wall thicknesses ranging from 0.078 to 0.150 in. Here we can put alloys like M1A, AZ3IB, AZ6IA, AZ80A, and ZK60A. The wrought compositions are aluminum, manganese, and zinc.
- M1A is used for various wrought manufactures including sheet, forgings, and extrusions. In any form, the strength of M1A is relatively low. It sheet is supplied as hot rolled or as cold rolled.
- AZ6lA and AZ80A find use for extrusions. Of the extrusion alloys, only AZ80A is not extruded into hollow shapes or tubing and we put it in category heat treatable.
- ZK60A is used for extrusions, too. ZK60A are heat treated by aging the material as fabricated.
Like other materials, magnesium alloys can be used in bolting, riveting, welding, screwing and sticky bonding. For example in bolting thick washers should be used under bolt heads and nuts to avoid damaging the flange or spot face. Screwed threads should be coarse with flat or rounded tops to avoid the notch effect. Important part of riveting must be purpose to crack or deform the magnesium around the rivet holes by using incorrect rivet lengths. Mechanical fasteners can be used on magnesium, provided that stress concentrations are held to a safe minimum. Only ductile aluminum rivets should be used, preferably alloy 5056-H32, to minimize galvanic-corrosion failure at riveted joints. Welding magnesium is mainly performed using the inert gas tungsten arc (TIG) and gas metal-arc (MIG) or argon arc techniques. The stretchable strength of an undressed butt weld made by the argon arc process usually exceeds 90 per sent of the parent material in the tempered state.