Y alloy is a

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

-containing aluminium alloy. It was developed by the British National Physical Laboratory during

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, in an attempt to find an aluminium alloy that would retain its strength at high temperatures. Duralumin, an aluminium alloy containing 4%

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

was already known at this time. Its strength, and its previously unknown age hardening behaviour had made it a popular choice for

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s. Aircraft of the period were largely constructed of wood, but there was a need for an aluminium alloy suitable for making engines, particularly

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...

s, that would have the strength of duralumin but could retain this when in service at high temperatures for long periods. The National Physical Laboratory began a series of experiments to study new aluminium alloys. Experimental series "Y" was successful, and gave its name to the new alloy. Like duralumin, this was a 4% copper alloy, but with the addition of 2% nickel and 1.5%

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

. This addition of nickel was an innovation for aluminium alloys. These alloys are one of the three main groups of high-strength aluminium alloys, the nickel–aluminium alloys having the advantage of retaining strength at high temperatures. The alloy was first used in the

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form, but was soon used for

forging Forging is a manufacturing process involving the shaping of metal using localized compression (physics), compressive forces. The blows are delivered with a hammer (often a power hammer) or a die (manufacturing), die. Forging is often classif ...

as well. One of the most pressing needs was to develop reliable pistons for aircraft engines. The first experts at forging this alloy were '' Peter Hooker Limited'' of

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, who were better known as The British Gnôme and Le Rhône Engine Co. They license-built the Gnome engine and fitted it with pistons of Y alloy, rather than their previous

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. These pistons were highly successful, although impressions of the alloy as a panacea suitable for all applications were less successful; a Gnôme cylinder in Y alloy failed on its first revolution. Banks, I Kept No Diary, p. 69 Frank Halford used

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s of this alloy for his de Havilland Gipsy engine, but these other uses failed to impress Rod Banks.

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Specification D.T.D 58A of April 1927 specified the composition and heat treatment of wrought Y alloy. The alloy became extremely important for pistons, and for engine components in general, but was little used for structural members of airframes. In the late 1920s, further research on nickel-aluminium alloys gave rise to the successful Hiduminium or "R.R. alloys", developed by

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Alloy composition

Heat treatment

As for many of the aluminium alloys, Y alloy age hardens spontaneously at normal temperatures after solution heat treating. The heat treatment is to heat it to for 6 hours, then to allow it to age naturally for 7–10 days. The precipitation hardening that takes place during this ageing forms precipitates of both CuAl₂ and NiAl₃. The times required depend on the grain structure of the alloy. Forged parts have the coarsest eutectic masses and so take the longest times. When cast, chill casting is favoured over sand casting as this gives a finer structure that is more amenable to heat treatment.

Alloy composition

Heat treatment

References

See also