4.2a metals and metallic alloys

What is a alloy

When two and more materials are combined and one of them is a metal, that makes an alloy

Extraction of metal from ore

A metal ore is a rock that contains metal or a metal compound, and its extraction depends on the level of reactivity of that metal.

Reactive metals are usually extracted by electrolysis

Less reactive are extracted by carbon or carbon monoxide

Aluminum extraction

aluminum ore most commonly bauxite is found in tropical and sub tropical areas, and it is refined into alumina and then electrolytically reduced into metallic aluminum

Extraction of pure metals out of ores

Common method is smelting and it is done by heating the ores in extremely high temperatures with the use of powerful furnaces

Steel

Steel is made by using oxygen furnaces and and electric arc furnaces

Grain size

in metal production, when the metal solidifies it rearranges into a metallic structure, and it can have three forms:

1. Close packed hexagon- weak, poor strength to weight ratio(like zinc and magnesium)

2. Face centered cubic- very ductile and a good electric conductor( like aluminum, gold, silver, copper, and lead)

3. Body centered cubic- hard and tough (like chromium)

Cooling in relation to grain size

Quick cooling - small grain

Slow cooling - large gain

Modifying mechanical properties by alloying

Alloying can make materials harder, lighter, cheaper, stronger

Advantages of alloying

• Changes the melting point

• Changes color

• Increases strength, hardness, and ductility

• Increases electric and thermal properties

Work hardening or cold working

The strengthening of a material by plastic deformation, and it makes the metal harder, while not using heat, the process includes:

• Rolling

• Bending

• Shearing

• Drawing

Annealing

Heat treatment that alters the physical and sometimes chemical properties of a metal making it more ductile and workable. Overall it is the process of softening the metal after work hardening

Case hardening

Making the outer shell harder, but maintaing the the inner core, so it stays flexible and relatively soft

Tempering

Heat treatment that increases toughness and reduces brittleness after quenching. Done after hardening to get rid of excess hardness

Supper alloys

Criteria:

• Creep resistance and at high temperatures, and excellent mechanical strength

• Resistance of oxidation and corrosion

creep resistance: gradual extension of materials under constant force, relies on temp and pressure

Oxidation resistance: does not rust easily

Application of super alloys:

Jet engine components

types of metals

There are two types:

1. Ferrous metals

2. Non ferrous metals

Ferrous metals

• Steel : ductile, tough, good tensile strength ,recycled, cheap(surgical tools, screw, nails)

• Iron: very ductile, strong, malleable, long lasting (tools, building structures, cars, machinery)

• Stainless steel: high intial cost, difficult to fabricate, difficult to weld due to high carbon(pipes, cutlery,aircraftj

Non ferrous metals

• Aluminum: light, malleable, conducts heat and electricity, corrosion resistant

• Brass:very corrosive, tarnishes, conducts electricity well

• Zinc: easily worked with, anti rust

• Tin: light, soft, corrosion resistant

• Copper: conducts heat and electricity, corrosion resistant, tough and ductile