Metals and alloys
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Apuntes de la lección
Types of metal
- Ferrous metals are iron-based, including mild and high-carbon steels, cast irons and stainless steels. Non-ferrous means iron is not the base metal, rather than an analytical guarantee of zero trace iron. Many ferrous materials are magnetic, but some stainless grades are not strongly attracted; some non-ferrous metals such as nickel are magnetic.
- Mild-steel grades can combine toughness, formability and weldability. Suitable hardened and tempered tool steels can retain an edge; cast-iron properties vary by grade and may suit cast shapes, wear resistance or damping. Avoid saying every cast iron is equally brittle or every steel has the same strength.
- Aluminium alloys can combine low density and useful mechanical properties; copper can offer electrical conductivity, ductility and useful pipework performance. Identify the grade and condition for the application. Non-ferrous metals do not form iron rust but can still corrode.
Classification does not define every property
Heat treatments
- Heat treatment changes microstructure and properties without simply changing the external shape. Suitable carbon and alloy steels can be quench-hardened after an appropriate controlled heating stage. Carbon content, alloy and process govern the response; ordinary mild steel or aluminium does not behave like high-carbon tool steel.
- Tempering suitable hardened steel adjusts the balance between hardness and toughness, generally reducing brittleness and some hardness. Annealing can soften or restore ductility; normalising suitable steels uses a different thermal cycle to influence structure. Schedules are material-specific rather than a universal colour or cooling rule.
- Case-hardening approaches develop a hard surface layer while retaining different core properties, sometimes by introducing carbon or nitrogen. This is a conceptual comparison of outcomes, not operational instructions, temperatures, quench-medium selection or a safe workshop procedure.
Selected steel: harden, then temper
Working and joining
- Forging uses compressive forces and can be hot or cold; casting solidifies molten material in a mould; rolling, bending and machining create different shapes through different mechanisms. Select the method using material, geometry, quantity, tolerance and finish requirements.
- Fusion welding melts the joint region, while solid-state welding joins without melting the parent materials. Brazing and soldering use molten filler while parent parts stay solid. Riveting and bolting form mechanical joints; a rivet normally must be destroyed for removal.
- A process name does not establish joint strength or safety. Suitable materials, joint design, surface preparation, process control and inspection matter. Explain the principle and application rather than treating a conceptual lesson as workshop authorisation.
Joining is more than melting all parts
Alloy composition and structure
- An alloy combines elements with at least one metal. Steel includes non-metal carbon, so an alloy is not necessarily a mixture of metals only. Brass is a copper–zinc family; traditional tin bronze is mainly copper and tin, with other bronze families also existing.
- Alloying can change hardness, strength, corrosion resistance and other properties, sometimes creating trade-offs. The copper–zinc diagram is a simplified substitution model showing unlike atoms in a metal lattice. It is not an exact composition, atomic-size comparison or crystallographic unit cell, and it does not prove every alloy is stronger than its host.
A simplified copper–zinc alloy
Corrosion and material selection
- Stainless steels contain chromium supporting a protective passive surface film; they can still corrode in unsuitable conditions. Magnetism, corrosion resistance and heat-treatment response vary by grade, so stainless is not one universal material property set.
- Galvanising places zinc on iron or steel, providing a barrier and sacrificial action under suitable conditions. Aluminium’s oxide can provide protection but does not make aluminium immune. Select grade, coating, detailing and maintenance for exposure instead of treating rust-free as an unconditional promise.
Explain protection without promising immunity
Diapositivas
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Preguntas de práctica
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1.What is a ferrous metal?
Easy- Aan iron-based metal or alloy
- Bone without iron
- Ca plastic
- Da timber
2.What is an alloy?
Easy- Aa pure metal
- Ba plastic
- Ca timber
- Da combination of elements, at least one being a metal
3.Which is a ferrous metal?
Easy- Acopper
- Bzinc
- Cmild steel
- Daluminium
4.Which is a non-ferrous metal?
Easy- Ahigh-carbon steel
- Bcopper
- Ccast iron
- Dmild steel
5.What is brass made of?
Easy- Acopper and zinc
- Bcopper and tin
- Ciron and carbon
- Dsteel and chromium
6.Which are the principal elements in traditional tin bronze?
Easy- Acopper and zinc
- Biron and carbon
- Csteel and chromium
- Dcopper and tin
7.What is stainless steel?
Easy- Acopper
- Bzinc
- Can iron-based chromium-containing alloy with grade-dependent corrosion resistance
- Dpure iron
8.What is a common purpose of an appropriate annealing treatment?
Easy- Apaints metal
- Bsoftening or restoring ductility, depending on the alloy and treatment
- Chardens metal
- Dmelts metal
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