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

The first of these Hiduminium alloys was termed 'R.R.50'. This alloy was first developed for motor-racing pistons, 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. 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. 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. 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, High Duty Alloys used it in their own advertising.

High Duty Alloys Ltd. was founded at Farnham Road, Slough in 1927, by Colonel W. C. Devereux. The company began from the ruins of the World War I aero engine builder, Peter Hooker Limited 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. 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.

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