CHAPTER V 

 THE SPECIAL BRASSES 



Many special or modified brasses have been devel- 

 oped to meet specific requirements. Nickel has been 

 added to produce desirable color characteristics, alumi- 

 num to improve corrosion-resisting properties, silicon to 

 improve hot-working properties and to increase tensUe 

 properties and electrical resistivity. Arsenic has been 

 added in more than trace amounts to improve tensile 

 strength and corrosion resistance. The more important 

 of the special brasses are 



1. The nickel brasses. 



2. Aluminum brass. 



3. Silicon brass. 



4. Arsenical brass. 



NICKEL BRASSES 



There is a wide commercial range of alloys of copper, 

 nickel, and zinc used primarily because of their color 

 characteristics. These alloys are known commonly as 

 the "nickel silvers" or "German silvers." A complete 

 discussion of the properties of these alloys wiU be found 

 in Chap. VI under Nickel Silvers. 



ALUMINUM BRASS 



In 1928 in the Eighth Report of the Corrosion Com- 

 mittee of the British Non-ferrous Research Association'^^', 

 data are given on an aluminum brass containing 76 per 

 cent of copper, 2 per cent of aluminum, and the balance 

 zinc. This alloy was developed specifically as a con- 

 denser-tube material for use under conditions of high 

 water velocity. Experimental evidence developed at 

 that time indicated that it possessed unusually good 

 resistance to the type of attack known as "impinge- 

 ment." Practical experience since that time with mil- 

 lions of pounds has thoroughly substantiated the 

 original conclusion. 



This aluminum brass was introduced to the United 

 States about 1930. Since that time an increasingly 

 large amount of this alloy in the form of condenser tubes 

 has been consumed annually by the heat exchanger 

 industry. It has been determined that the inclusion of 

 2 per cent of aluminum with 77 per cent of copper pro- 

 duced an alloy with mechanical and structural properties 

 closely approximating 70-30 brass. It further had been 

 proved that the aluminum conferred on the brass the 

 property of forming quickly when exposed to corrosive 

 media such as salt or brackish water, a highly protective 

 film that was tenacious, impervious, and self-healing. 



Aluminum-brass condenser tubes are used extensively 

 in this country for handling salt or brackish waters in 

 both stationary and marine condensers where cooling 

 water velocities are high. 



In the development of this alloy it was found desirable 

 to maintain an arsenic content of from 0.02 to 0.05 per 

 cent. The function of the arsenic is to prevent dezincifi- 

 cation particularly during stand-by periods. Since 

 arsenic acts as an oxygen carrier, the presence of the 

 above amount in aluminum brass also renders it more 

 resistant to pitting as a consequence of oxygen-concen- 

 tration cell action. 



A summarization of mechanical properties and the 

 most important physical properties may be found in 

 Table 1. Complete mechanical properties in the 

 annealed and at elevated temperatures may be found on 

 page 177. 



SILICON BRASSES 



An investigation on the effect of silicon on copper-zinc 

 alloys containing up to 70 per cent of copper was first 

 made by Guillet in 1909. He determined that 1 per 

 cent of silicon exercised as much effect structurally as 

 10 per cent of zinc. Although his work indicated that 

 there were many interesting alloys possible, there was 

 little if any commercial interest shown in the silicon 

 brasses until about 1935. 



With the development of refrigeration, particularly 

 as it pertained to domestic installations, a need arose 

 for a material of moderate cost, which could be fabri- 

 cated economically, would possess reasonably good cor- 

 rosion resistance, and could be spot- or seam-welded. 

 After considerable experimental effort, on the part of 

 both metal fabricators and refrigerator manufacturers, 

 two silicon brasses were developed. These alloys are 

 the only ones in commercial use today. One of these 

 contains 77 per cent of copper, 1 per cent of silicon, and 

 the balance zinc ; the other contains 70 per cent of copper, 

 0.50 per cent of silicon, and the balance zinc. 



The higher copper-silicon brass has been the most 

 popular since it possesses physical properties and spot- 

 and seam-welding characteristics very closely approxi- 

 mating those of the silicon coppers, which in turn, by 

 reason of their low electrical conductivity, approach the 

 performance of mild steel. <^^' 



More recently, primarily because of economic reasons, 

 the lower copper-silicon brass has been used more exten- 

 sively in the manufacture of evaporators for refrigerators. 



Both of these alloys possess better hot-working prop- 

 erties than equivalent copper-zinc alloys and, in addition, 

 are nearly as plastic in the cold condition as their copper- 

 zinc alloy counterpart. These two alloys are usually 

 supplied in sheet and strip form. Because of the pres- 

 ence of the silicon, specialized methods for cleaning or 

 removing oxide scales, produced during annealing oper- 



175 



