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  • In the early days of flight, engineers relied on building materials like wood and canvas

  • to build their planes. The Wright Brothers worked tirelessly to reduce the weight of

  • their aircraft to allow it get off the ground. They used woods with high strength to weight

  • ratios like spruce and ash to build their frame, but it needed to be reinforced with

  • steel wire to prevent the frame from bending under flight loads. The flight surfaces were

  • covered in lightweight fabric to provide a smooth aerodynamic surface. But one of their

  • greatest innovations was the construction of their engine. No engine existed at this

  • time that matched their power to weight requirements, so they went about inventing their own.

  • They were the first in history to use Aluminium as a building material for an engine, using

  • it to construct their crankcase. They even painted the engine black, so their competitors

  • couldn’t see that the engine was built using aluminium.

  • Aluminium makes up 8% of the earth’s crust. Despite that, it used to be one of the world's

  • most expensive materials. It is a difficult material to refine. Napoleon had envisioned

  • the lightweight metal as the perfect material for weapons and armour, but became frustrated

  • with the difficulty of the refining process. Finally giving up, he had his small supply

  • of aluminium melted down and made into cutlery and plates to serve his most esteemed guests,

  • while the lower ranks were resigned to the less expensive Gold pieces.

  • It wasn't until the 1880s that methods capable of mass producing the material were developed.

  • In a few short years, aluminium went from being the most expensive metal on Earth to

  • one of the cheapest. Dropping in price from $1200 per kilo in 1852 to just one dollar

  • per kilo at the start of the 20th century. This paved the way for the Wright Brothers

  • to use the material in the Wright Flyer, but the material the Wrights used was very different

  • to the Aluminium alloys we see today. Despite the availability of aluminium, planes throughout

  • world war 1 continued to use wood and canvas as their primary building materials, because

  • the aluminium that was available back then, was a weak and malleable.

  • An accidental discovery of a new heat treatment by the German scientist Alfred Wilm led to

  • the development of an aluminium alloy strong enough for structural use. Alfred was trying

  • to recreate the effects of quench hardening that is seen with iron alloys like steel,

  • you see this process a lot in the awesome Man at Arms series, after heating the steel

  • between 700 and 900 degrees they will quench the blade in oil or water, this rapidly cools

  • the steel, which causes a crystalline structure called martensite to form, which is much harder

  • than the crystal structure that would form if it was allowed to cool slowly. But this

  • technique does not work with aluminium.

  • As the story goes, one Friday afternoon Alfred was testing a new alloy of aluminium he had

  • developed, containing about 4% copper. He followed the steps for quench hardening. He

  • heated the metal up and allowed the heat to evenly distributed throughout the material,

  • he then removed the metal from the heat and quenched it, rapidly cooling it. He then tested

  • the material, but it showed no real sign of improvement. Becoming frustrated he left the

  • lab, leaving the remaining samples, resting at room temperature over the weekend.

  • To his amazement, when he returned the following Monday he discovered the remaining samples

  • had grown stronger. Alfred Wilm had just accidentally discovered age hardening. A process that would

  • make aluminium the world’s new wonder material.

  • So what happened here, why did the new alloy get stronger over time? To understand this

  • we need to look at the metal’s crystalline structure.

  • This is a single aluminium atom. Now if it is joined by more atoms they don't just arrange

  • randomly, they form regular patterns with a repeating structure. Aluminum forms a repeating

  • crystal structure called face centred cubic which looks like this and it defines many

  • of the properties of the material. One of these properties is direction it most easily

  • deforms, for example this crystal structure deforms most easily along this plane. This

  • is called a slip plane.

  • Let’s look at a 2D cubic structure like this, it can easily slip in these parallel

  • directions, so if a force is applied here with sufficient force each atom will shift

  • down and the material will permanently deform, but this material is pure aluminium. What

  • happens when we swap some of these aluminium atoms for copper.

  • Copper atoms are slightly larger than aluminium and they create internal strain when fitting

  • into aluminium crystal lattice. When the alloy was heated, the copper spread evenly through

  • the material and the quenching process trapped the copper in these locations. In these positions,

  • the copper atoms do not provide much strength. But over time they begin to coalesce to form

  • these secondary crystal structures within the main crystal structure, this is a called

  • a second phase. These second phase particles create barriers to deformation, for deformation

  • to occur a much greater force is needed.

  • In the following years Alfred perfected this process, figuring out the ideal aging temperature

  • and time. He dubbed his new material Duralumin and it was used to build the world’s first

  • all metal aircraft the Junkers J1.

  • The impact of this age hardened aluminium had cannot be understated, it completely transformed

  • our world. Prior to its introduction , planes frames were all built with rigid truss structures,

  • like this. With aluminium at their disposal, engineers could create a new type of flight

  • structure, the monocoque and semi-monocoque. With these frames the aluminium skin forms

  • an integral part of the planes strength, not just being used as a streamlined flight surface.

  • These new techniques freed up space within the planes and allowed spacious passenger

  • planes to be developed, ushering in a new era of travel in the world.

  • 13% of the world’s aluminium is used by the energy sector, even though copper is a

  • better conductor, all main overhead power lines use aluminium as the conducting material.

  • To carry the same current as a copper wire an aluminium wire needs to 1.5 times thicker

  • and even then it is still two times lighter. This decreases the load on pylons and allows

  • the spans between them to increase dramatically. This saves vasts amount of money on construction.

  • 23 % of aluminium is used in construction. The Empire State Building was the world’s

  • first skyscraper to use the material extensively. It’s corrosion resistance and lightness

  • made it the perfect material for exterior framing and roofing.

  • It’s clear to see, without this material the world we see today would be very different

  • and only recently has aluminium started to see competition from composite materials like

  • carbon reinforced plastics, but that’s a topic for another day.

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  • put this message at the end, but I don't believe in getting something for nothing. So please

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  • below.

In the early days of flight, engineers relied on building materials like wood and canvas

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B2 中高級 美國腔

铝——改变世界的材料(Aluminium - The Material That Changed The World)

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    joey joey 發佈於 2021 年 06 月 05 日
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