Properties and Uses of Metals in Engineering
Iron
Iron has high thermal and electrical conductivity and is a special magnetic element. It exhibits great malleability and ductility, with a fusion temperature of 1537ºC. However, it is vulnerable to oxidation.
Aluminum
Aluminum is soft and has low mechanical strength. Its fusion temperature is relatively low, between 650ºC and 750ºC. Aluminum is frequently used in light alloys to achieve the minimum weight possible with acceptable mechanical strength. It is combined with magnesium and titanium to form these alloys.
Copper
Copper is the best conductor of electricity and heat. It is resistant to corrosion and oxidation, ductile, malleable, and a very soft metal. Its main use is in wiring. Brass, an alloy of copper, is harder than pure copper, easy to machine, and resistant to oxidation.
Steel
Steel has excellent mechanical strength but is susceptible to oxidation and is heavy. Its fusion temperature is often around 1500ºC. High-strength steels are alloys of chromium, vanadium, and titanium, offering three times more resistance to deformation.
- German Steel: High yield, elasticity, and low weight. Good behavior in deformation.
- Stainless Steels: High hardness and high resistance to wear and oxidation. Used in areas with a high risk of oxidation.
Castings
Castings are alloys of iron with a carbon ratio between 1.7% and 6.5%. They are easy to machine, have good resistance to corrosion, wear, and vibration, but are more brittle than steel and difficult to weld.
Thermal Treatments
Quenching
Quenching involves heating and rapidly cooling steel. The objective is to increase hardness and brittleness.
Annealing
Annealing is the process of heating steel to a constant temperature for a specified period, followed by gentle and moderated cooling. It softens the steel.
Tempering
Tempering reduces internal stresses, decreases the fragility of the metal, and slightly reduces hardness. Steps include heating below the quenching temperature, maintaining the temperature, and slow cooling.
Normalizing
Normalizing involves heating the metal to the hardening temperature and maintaining it for a while. Cooling is neither very fast nor very moderate.
Metalworking Operations
Casting
Casting involves pouring molten metal into molds. Metals are subjected to high temperatures until they melt.
Forging
Forging is shaping metal by hammering it after it has been heated.
Stamping
Stamping is used to create deep, hollow shapes in metal using punches and pressure. The material must be malleable.
Physical Properties
Dilatability
Dilatability is the property of a metal to increase its volume due to gentle warming.
Fusibility
Fusibility is the change of physical state of a metal from solid to liquid.
Mechanical Properties
Hardness
Hardness is the resistance of a body to deformation.
Elasticity
Elasticity is the property of metals to recover their shape or size.
Yield strength is the force applied in a trial.
Tenacity
Tenacity is the property of a material to resist breakage and distortion.
Fragility
Fragility is the opposite of tenacity.
Plasticity
Plasticity is the opposite of elasticity. If the metal facilitates the processing of yarns, it is called ductility; if it facilitates processing into sheets, it is called malleability.
Testing of Metals
The mechanical behavior of materials is their response to stress.
Match tests include characteristic, destructive, non-destructive, and technological tests.
Traction Test
A traction test involves subjecting a standard specimen to tension.