Six cylinder, 5 litre, all-Hiduminium engine for the Armstrong Siddeley Special

The Hiduminium or R.R. alloys are a series of high-strength, high-temperature aluminium alloys, developed for aircraft use by Rolls-Royce before World War II.[1] They were manufactured and later developed by High Duty Alloys Ltd..[1] The name Hi-Du-Minium is derived from that of High Duty Alloys.

The first of these Hiduminium alloys was termed 'R.R.50' .[1] This alloy was first developed for motor-racing pistons,[2] and was only later adopted for aircraft engine use. It was a development of the earlier Y alloy, the first of the nickel-containing light aluminium alloys.[3] 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, making them particularly useful for pistons.


Early adoption

The alloys were in limited use for aircraft by 1929, being used in the Rolls-Royce R engine that was successful in the Schneider Trophy seaplane races. They quickly spread to other manufacturers, in 1931 being adopted by ABC for their Hornet engine.[4] R.R.50 alloy was used for the crankcase, R.R.53 for the pistons.

Their first mass production use was in the Armstrong Siddeley Special saloon car of 1933.[2] Armstrong Siddeley already having had experience of the alloy, and financial investment in its manufacturer, from their aero engine business.

Advantages of these alloys were recognised worldwide. When 576 pistons in Hiduminium R.R.59 alloy were used for the Italian Marshal Balbo's trans-Atlantic flight,[5] High Duty Alloys used it in their own advertising.[6]

High Duty Alloys Ltd.

High Duty Alloys Ltd. was founded at Farnham Road, Slough in 1927.[7]

The company began from the ruins of the World War I aero engine builder, Peter Hooker Ltd. of Walthamstow.[8] Hookers license-built the Gnôme engine and were better known as The British Gnôme and Le Rhône Engine Co.[9] They had become expert at working Y alloy.[10] After some years in voluntary liquidation, the company was wound up in 1927. Simultaneously a large order was received, of some thousands of pistons for the Armstrong Siddeley Jaguar engine. Armstrong Siddeley had no other capable source for these pistons, so W.C. Devereux, works manager of Hookers, proposed to set up a new company to complete this order. John Siddeley loaned the money to re-purchase the necessary equipment and re-employ some of the staff from Hookers.[8] As the buildings had already been sold, the new company relocated to Slough.

Demand from Rolls-Royce later led to expansion into a factory at Redditch. These materials were so crucial to aircraft production that with the outbreak of World War II a shadow factory was established in the remote area of Westmoreland (now Cumbria), at Distington, near Whitehaven.[7]

As well as producing ingots of raw alloy, manufacturing included the initial forging or casting processes. Finish machining would be undertaken by the customer. Hiduminium was so successful that during World War II it was in use by all of the major British aero engine makers.

In 1934 the Reynolds Tube Co. began production of extruded structural components for airframes, using R.R.56 alloy supplied by High Duty Alloys. A new purpose-built plant was constructed at their works in Tyseley, Birmingham.[11] In time, the post-war Reynolds company, already known for its steel bicycle frame tubes, would attempt to survive in the peacetime market by supplying Hiduminium alloy components for high-end aluminium bicycle cranks and brakes.[12]

The 1,600 torches for the 1948 London Olympics were cast by the company.[13]

Alloy composition

The Duralumin alloys had already demonstrated high-strength aluminium alloys. Y alloy's virtue was its ability to maintain high strength at high temperatures. R.R alloys were developed by Hall & Bradbury at Rolls-Royce,[3] partly to simplify the manufacture of components using them. A deliberate heat treatment process of multiple steps was used to control their physical properties.

In terms of composition, Y alloy typically contains 4% of copper and 2% of nickel. R.R. alloys reduce each of these by half to 2% and 1%, and 1% of iron is introduced.

Example composition:

R.R.56 [1]
Melting point 635°C
Density 2.75
Copper 2.0%
Nickel 1.3%
Magnesium 0.8%
Iron 1.4%
Titanium 0.1%
Silicon 0.7%
Aluminium 93.7%

Heat treatment

As for many of the aluminium alloys, Y alloy age hardens spontaneously at normal temperatures after solution heat treating. In contrast, R.R. alloys remain soft afterwards, until deliberately heat treated again by precipitation hardening for artificial ageing.[3] This simplifies their machining in the soft state, particularly where component blanks are made by a subcontractor and must be shipped to another site before machining. For R.R.56 the solution treatment is to quench from 530°C and ageing is carried out at 175°C.[3] For R.R.50, the solution treatment may be omitted and the metal taken directly to precipitation hardening (155°C-170°C).[14]

After solution treatment, the tensile strength of the alloy increases, but its Young's modulus decreases. The second stage of artificial aging increases the strength slightly, but also restores or improves the modulus.[15]

R.R.53 B, chill cast [15]
Maximum Stress
Tons/sq in.
As cast 14 3%
Solution treated 22 6%
Solution treated
and artificially aged
26 3%
Composition, R.R.53 B [15]
Copper 2.5%
Nickel 1.5%
Magnesium 0.8%
Iron 1.2%
Silicon 1.2%
Aluminium 92.8%

Alloy range

A range of alloys were produced in the R.R.50 range.[16] These could be worked by casting or forging, but they were not intended for rolling as sheet or general machining from bar stock.

R.R. 50 General-purpose sand casting alloy
R.R. 53 Die-cast piston alloy
R.R. 56 General-purpose forging alloy
R.R. 59 Forged piston alloy

The number of alloys expanded to support a range of applications and processing techniques. At the Paris Airshow of 1953, High Duty Alloys showed no less than eight different Hiduminium R.R. alloys: 20, 50, 56, 58, 66, 77, 80, 90.[17] Also shown were gas turbine compressor and turbine blades in Hiduminium, and a range of their products in the Magnuminium alloy series.

R.R.58, comprising 2.5 copper, 1.5 magnesium, 1.0 iron, 1.2 nickel, 0.2 silicon, 0.1 titanium and the remainder aluminium, and originally intended for jet engine compressor blades, was used as the main structural material for the Concorde airframe, supplied by High Duty Alloys, it was also known as AU2GN to the French side of the project[18]

Later alloys, such as R.R.66, were used for sheet, where high strength was needed in an alloy capable of being worked by deep drawing.[19] This became increasingly important with the faster jet aircraft post-war, as issues such as transonic compressibility became important. It was now necessary for an aircraft's covering material to be strong, not merely the spar or framing beneath.

R.R.350, a sand-castable high temperature alloy, was used in the General Electric YJ93 jet engine and was also used in the General Electric GE4 intended for the later cancelled American Boeing 2707 SST project.[20]

External links


  1. ^ a b c d FJ Camm (January 1944). "R.R. Alloys". Dictionary of Metals and Alloys (3rd ed.). pp. 102. 
  2. ^ a b FJ Camm (January 1944). "Hiduminium". Dictionary of Metals and Alloys (3rd ed.). pp. 58. 
  3. ^ a b c d Murphy, A.J. (1966). "Materials in Aircraft Structures". J. Royal Aeronautical Society 70 (661): 117. ISSN 0368-3931. 
  4. ^ "ABC 'Hornet' Modified" (PDF). Flight: 335. 17 April 1931. http://www.flightglobal.com/pdfarchive/view/1931/1931%20-%200359.html. 
  5. ^ A fleet of twenty-four Savoia-Marchetti S.55 flying boats, each with two tandem V-12 engines, flew to the Chicago Century of Progress exposition.
  6. ^ "Another Triumph for Hiduminium" (advert). Flight. 14 September 1933. http://www.flightglobal.com/pdfarchive/view/1933/1933%20-%200553.html. 
  7. ^ a b "High Duty Alloys Ltd, Distington". http://www.archiveweb.cumbria.gov.uk/dserve/dserve.exe?dsqIni=Dserve.ini&dsqApp=Archive&dsqDb=Catalog&dsqCmd=Show.tcl&dsqSearch=(RefNo==%27YDB%2068%27). 
  8. ^ a b Banks, Air Commodore F.R. (Rod) (1978). I Kept No Diary. Airlife. pp. 71. ISBN 0-9504543-9-7. 
  9. ^ Banks, I Kept No Diary, p. 63
  10. ^ FJ Camm (January 1944). "Y alloy". Dictionary of Metals and Alloys (3rd ed.). pp. 128. 
  11. ^ "Hiduminium for Aircraft" (PDF). Flight: 1070. 11 October 1934. http://www.flightglobal.com/pdfarchive/view/1934/1934%20-%201068.html. 
  12. ^ Hilary Stone. "G B brakes (Gerry Burgess Cycle Components, 1948)". http://www.classiclightweights.co.uk/designs/hs-gbrakes.html. 
  13. ^ "1948 Olympics" (PDF). Flight: 90. 22 July 1948. http://www.flightglobal.com/pdfarchive/view/1948/1948%20-%201112.html. 
  14. ^ Higgins, Raymond A. (1983). Part I: Applied Physical Metallurgy (5th ed.). Hodder & Stoughton. pp. 435–438. ISBN 0-340-28524-9. 
  15. ^ a b c "Aircraft Engineer, 25 January 1934, Hiduminium R.R.53 B" (PDF). The Aircraft Engineer, (supplement to Flight): 8. 25 January 1934. http://www.flightglobal.com/pdfarchive/view/1934/1934%20-%201396.html. 
  16. ^ "Hiduminium R.R. alloys" (PDF). Flight: 84. 22 January 1932. http://www.flightglobal.com/pdfarchive/view/1932/1932%20-%200084.html. 
  17. ^ "Britain at the Paris Airshow" (PDF). Flight: 808. 26 June 1953. http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%200814.html. 
  18. ^ http://heritageconcorde.com/?page_id=469
  19. ^ "Hiduminium R.R.66 advert featuring DH Comet" (advert). Flight. 13 March 1959. http://www.flightglobal.com/pdfarchive/view/1959/1959%20-%200706.html. 
  20. ^ Gunderson, Allen W. (February 1969). "Elevated Temperature Mechanical Properties of Two Cast Aluminum Alloys". Air Force Materials Laboratory, Wright-Patterson AFB. AFML-TR-69-100. http://docs.google.com/viewer?a=v&q=cache:xbW4lCRwD5YJ:www.dtic.mil/cgi-bin/GetTRDoc%3FLocation%3DU2%26doc%3DGetTRDoc.pdf%26AD%3DAD0860080+hiduminium&hl=en&gl=uk&pid=bl&srcid=ADGEEShjCYQN6TpRSAk3pzxsL5ryL7hYv0b6a5aBUoc6rInzHIz6fsst48eca3ZhIy6BJ2UH9ZRnXA7dgR_JVLtFaS7a9bpbwhSvZeyuLlPCLa9WSvHRRfVhUw_rM2JOs66kevfJ6Um9&sig=AHIEtbRvyW2JxqEU_JOUTp7ymGr2hHA9xQ. 

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