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The Hiduminium alloys or R.R. alloys are a series of high-strength, high-temperature , developed for aircraft use by Rolls-Royce ("RR") before World War II.
The first of these Hiduminium alloys was termed
Their first mass production use was in the Siddeley Special Six saloon car of 1933. Armstrong Siddeley already having had experience with 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 Italo Balbo's trans-Atlantic flight,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. High Duty Alloys used it in their own advertising.
The company began from the ruins of the World War I aero engine builder, Peter Hooker of Walthamstow. Hookers licence-built the Gnôme engine, amongst other things, and for the aero engines chose to be known as The British Gnôme and Le Rhône Engine Co.Banks, I Kept No Diary, p. 63 They had become expert at working Y alloy. The post-war reduction in demand and the plentiful supply of war-surplus engines made times hard for all engine and component makers. After buying it at the beginning of 1920 BSA reviewed its operations and decided Hooker's should be liquidated. After some years in voluntary liquidation, Hooker's operations ended in late 1927 when its workshops were sold.
About that time 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 Hooker, 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 Hooker. As the buildings had already been sold, the new company found premises in 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 Cumberland (now Cumbria), at Distington, near Whitehaven.
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. 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 crankset and bicycle brake.
The impeller (compressor) and compressor casing of the 1937 Power Jets WU jet engine was made from RR.56 and RR.55 respectively. In the subsequent Power Jets W.1 the compressor material was changed to RR.59. By 1943 the de Havilland Goblin, the first British production jet engine to be built in large numbers, was in development. The centrifugal compressor for this began as a 500 lb 'cheese' of RR.50, the largest forging made of it. After machining, these were reduced to 109 lbs. The size of this forging was so great that cooling rates in its centre affected the metallurgical properties of the alloy; Devereux advised the reduction of the silicon content to below 0.25% and this low silicon RR.50 alloy was used throughout Goblin production.
The 1,600 Olympic torch for the 1948 London Olympics were cast by the company.
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 |
| 635 °C |
| 2.75 |
| 93.7% |
| 2.0% |
| 1.4% |
| 1.3% |
| 0.8% |
| 0.7% |
| 0.1% |
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.
| + R.R.53 B, chill cast |
| 3% |
| 6% |
| 3% |
| + Composition, R.R.53 B |
| 92.8% |
| 2.5% |
| 1.5% |
| 1.2% |
| 1.2% |
| 0.8% |
| General-purpose sand casting alloy |
| Additional silicon content, to improve flow when machine casting |
| General-purpose forging alloy |
| Low-creep forging alloy for rotating impellers and compressors |
| 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. Also shown were gas turbine compressor and in Hiduminium, and a range of their products in the Magnuminium alloy series.
R.R.58, also known as Aluminium 2618, 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.
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. 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.
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