  The homogeneous data sets for the calcium and scandium abundances accounting
for departures from LTE were obtained for a sample of 54 metallic-line (Am)
stars. The Ca and Sc abundances were found to correlate with effective
temperature Teff, the abundance growth with increasing Teff being higher in
stars with surface gravity log g < 4 than in those with log g > 4. No
correlation was found between Ca or Sc abundances and the iron abundance or the
velocity of axial rotation. Am stars exhibit on average the higher values of
[Ca/H] than those of [Sc/H] as well as the abundance ratio [Ca/Sc] = 0.41 +/-
0.30. However, at Teff > 9500 K there is an allusion to the systematic
difference between Am stars with surface gravity log g > 4 and log g < 4. The
iron excess is nearly the same in the range 7200 K <= Teff <= 10030 K.
Evolution diffusion models computed with the code MESA for stars with masses
from 1.5 to 2Msun show the surface abundances that are in good agreement with
Ca and Fe abundances observed in Am stars of the three open clusters with the
age > 600 Myr. Additional mechanisms of chemical separation should be
considered for explanation of the Am phenomenon in young stars of the Pleiades
cluster. We tested the published diffusion stellar evolution models. The
diffusion models by Richer et al. (2000) and Hui-Bon-Hoa et al. (2022) are
shown to agree with observations of Am stars in the open clusters at large
values of the free turbulence parameter: omega=1000 for Ca and Fe, omega=500
for Sc. There is no model with the mass and age of the Am-type star Sirius that
could reproduce its surface abundances from He to Ni. The results presented in
the paper may be of importance for understanding the chemical peculiarity of Am
stars.
