time in the copper sulfate spot test for the phosphating layer is
listed in Table 2.
Table 2 showed that the phosphating temperature significantly
affected the corrosion resistance. Curve A is higher than curve B in
Fig. 4, which also displays that a high corrosion resistance for
phosphating layer needs long phosphating duration at a low
phosphating temperature. Therefore, the recommended phosphating
time was 3 min at temperature higher than 20 C, 5–7 min
at a temperature ranging from 10 to 20 C, and 7–25 min at
a temperature ranging from 3 to 10 C. The corrosion resistance for
the phosphating layers increased with an increase in phosphating
temperature, therefore, room temperature ranging from 10 to 35 C
was recommended when this innovative phosphating solution was
used, although 3 C was also acceptable.