CHAPTER IX 

 THE ALUMINUM BRONZES 



Aluminum bronzes are high-copper alloys with alumi- 

 num, most commonly containing between 4 and 10 per 

 cent of aluminum. Additions of iron, nickel, silicon, 

 and manganese are frequently made to the alloys of 

 higher aluminum content to increase strength and 

 hardness. 



The industrial use of the aluminum bronzes has untU 

 recently been largely restricted to castings for acid- 

 resisting parts. Difficulties in the fabrication of wrought 

 aluminum bronzes have greatly retarded their extensive 

 application. Developing technique and improved man- 

 ufacturing facilities are gradually rendering wrought 

 forms of these alloys more readily available. 



Industrial aluminum bronzes are of two general types: 

 the alpha or single-phase alloys — often referred to as 

 homogeneous alloys; and the alpha-beta, or two-phase 

 alloys — known commercially as duplex bronzes. Under 

 perfect equilibrium conditions 9.8 per cent of aluminum 

 is soluble ia copper before the beta phase appears, but 

 in commercial practice perfect equilibrium conditions 

 are practically never reached, and alloys containing in 

 excess of 7.5 per cent of aluminum usually exhibit two 

 phases. 



The alpha aluminum bronzes possess excellent cold- 

 working properties. They also have good hot-working 

 properties and can be readily hot-forged, rolled, and 

 extruded. They are most plastic within a temperature 

 range of 1450 to 1650°F. Their hot plasticity increases 

 as the aluminum content increases and, conversely, their 

 cold-working properties decrease with a corresponding 

 increase in sensitivity to work hardening. 



The duplex bronzes have excellent hot-working proper- 

 ties through a much wider range than the alpha bronzes. 

 They can be extruded and hot-forged into very intricate 

 shapes. Their hot-working properties compare very 

 favorably to the alpha-beta brasses but like the latter 

 alloys they can be cold-worked only lightly. Generally, 

 these aluminum bronzes are furnished in the hot-rolled 

 or extruded condition. Occasionally, however, they 

 are given light cold-working operations for the purpose 

 of obtaining dimensional accuracy. Hot working is 

 usually performed within a temperature range of 1300 

 to 1650°F., depending on the alloy composition and 

 the amount of plastic flow required. 



The alpha aluminum bronzes have tensile properties 

 comparable to the high brasses and possess the maximum 

 ductility of any of the aluminum bronzes. However, 

 they work-harden rapidly and are not generally used for 

 severe drawing or stamping operations. 



Duplex alloys possess very high tensile strength, but 

 are lacking in ductility. These alloys in the heat- 

 treated or hot-worked condition have tensile properties 

 comparable to the work-hardened silicon bronzes. 



The annealing characteristics of the alpha aluminum 

 bronzes are similar to those of the alpha brasses and 

 softening of work-hardened alloys can be accomplished 

 by annealing within the temperature range of 800 to 

 1400°F., depending upon the properties required. 



The duplex bronzes are capable of being heat-treated 

 for the general improvement of mechanical properties 

 and are usually furnished or used in this condition. 

 Heat-treatment of these alloys consists of quenching ia 

 water from temperatures of 1500 to 1600°F. and reanneal- 

 ing between 700 and 1100°F., according to the thickness 

 of the section and composition of the alloy. 



All the aluminum bronzes possess good resistance to 

 scaling or oxidation at elevated temperatures, being 

 better in this respect than any of the other copper-base 

 alloys. The resistance to scaling or oxidation increases 

 with the aluminum content. 



The resistance of the aluminum bronzes to corrosion 

 is largely due to the formation on their exposed surface 

 of aluminum oxide (AI2O3). Because this film is very 

 resistant to attack by mineral acids, aluminum bronzes 

 have been widely used in constructions requiring resis- 

 tance to the action of such acids. Since, however, this 

 film is soluble in alkalies, aluminum bronzes offer but 

 mediocre resistance to the attack of strong alkalies. 

 Resistance of aluminum bronzes to acid attack tends to 

 increase with increasing aluminum content. Under 

 certain conditions of corrosion the alpha-beta aluminum 

 bronzes are susceptible to a form of corrosion that is 

 analogous to " dezincification " in brass and has been 

 called "dealuminization." 



The alpha bronzes, either plain or modified with up to 

 4 per cent of nickel to increase resistance to salt- or 

 brackish-water corrosion, have shown signs of being suit- 

 able for use in oU-refinery service, and other heat- 

 exchanger fields, as condenser tubes and tube plates. 

 The alloy containing 5 per cent of aluminum is commer- 

 cially available in the form of strip, rod, and tube. 



This alloy has a very pleasing golden color approxi- 

 mating that of 18-karat gold and has found some applica- 

 tions in the costume-jewelry field, for radio faces, and 

 decorative emblems. 



In general the wrought aluminum bronzes are used in 

 those applications requiring high tensile properties in 

 combination with good corrosion resistance; in such 

 parts as valve stems, propeller-blade bolts, air pumps, 

 condenser bolts, and for other purposes requiring high 

 strength in combination with good wear-resisting proper- 

 ties, such as slide liners and bushings. The physical 

 and general mechanical properties of the more common 

 aluminum bronzes may be found in Tables 1 to 4 on 

 pages 254 to 263. Charts 1 to 35 on pages 255 to 265 give 

 more detailed data. 



