22 Mr. R. L. Wills on the Effects of Temperature 



Aluminium Alloy. 



Investigations on the magnetic behaviour of alloys of iron 

 have shown that the influence of aluminium is of an entirely 

 different nature to that of most other elements. 



Perhaps the most striking difference is seen between the 

 effects of chromium or tungsten and aluminium. 



The effect on the magnetic properties of iron of adding 

 even a small percentage of tungsten is to increase considerably 

 both the retentivity and coercive force, while the addition of 

 a small percentage of aluminium has just the opposite effect. 

 The maximum magnetization in each case is fairly high, but 

 the permeability for the tungsten alloy is very small, while 

 for the aluminium alloy it compares very favourably with 

 that of the best iron. 



From these considerations it appeared desirable to inves- 

 tigate the effect of heat on the magnetic properties of an 

 aluminium alloy. 



Richardson * has examined the effect of temperature on 

 certain aluminium alloys, and drawn curves showing the 

 change in induction with rise of temperature for different 

 magnetizing forces. 



The results of experiment given for an alloy containing 

 3'64 per cent, aluminium show that at the ordinary tem- 

 perature the permeability is low, and, upon heating, the 

 induction increases, reaching a maximum at a temperature of 

 about 380° C; the permeability decreases with rise of tem- 

 perature near the critical point until a minimum value is 

 reached, when further heating but slightly affects the 

 permeability. 



Other investigations f on the influence of elements on the 

 magnetic properties of iron have shown that the addition of 

 between 2 per cent, and 3 per cent, of aluminium has very 

 little effect on the maximum induction, and that the per- 

 meability for low magnetizing forces is even higher than 

 that of a good specimen of iron. It is also shown that when 

 the percentage of aluminium is increased to 5*5 per cent, the 

 maximum induction is fairly high, and the permeability for 

 weak forces only slightly affected. 



Experiments similar to those described above were made on 

 an aluminium alloy of the follow ing composition. The analysis 



* Phil. Mag. January 1900, pp. 121-154. 



t Barrett, Brown and Hadfield: " The Electrical Conductivity and 

 Magnetic Permeability of various Alloys of Iron," Trans. Roy. Dublin 

 Soc. vol. vii. Jan. 1900, p. 116. 



