To determine the resistance of the coatings of Zn / Al and Al have been performed numerous tests in salt mist with the presence of NaCl 5% the temperature of 35 ° C + 2 °C. The loss of thickness of coatings detected after 168 hours of exposure showed the results shown in Figure 14.
The results demonstrate that the addition of Al to zinc greatly improves the resistance of the zinc. The best result is obtained with the Zn / Al 85-15, which has a resistance to corrosion 10 times higher than pure zinc. Increasing the presence of’ In addition to the 15% however, we are witnessing the growth of pitting. Vedi figura 15.
The onset of red rust (fig. 16) occurs after 300-500 hours for zinc and after 500-900 hours for alloys Zn / Al. As for the pure Al occurs after the appearance just 50 hours.
| By extending the results found, we can deduce a rule of thumb: | ||||
| Loss in thickness after 168h | ||||
| Thickness loss | Resistance in h | Thickness loss | Resistance in h | |
| Zn puro | 20µ | 300-400h | 80µ | 1.200-1.400h |
| Zn/Al 85-15 | 2,0µ | 500-900h | 80µ | 2.000-3.600h |
And’ Note that the salt spray test carried out in the environment of high electrolytic conductivity have proven ineffective for the coatings of sacrificial nature such as zinc which has high properties anodic. For this reason, The researchers further reservations about the value of the salt spray test because in practice we must take account of the real environment where the atmosphere alternating wet and dry phases with low presence of electrolytic conductivity.