  We report data on the thermal conductivity K(T,H) along the basal plane of
the hexagonal crystal structure of superconducting Mg{1-y}Al{y}B2 with y=0.02
and 0.07 at temperatures between 0.5 and 50 K and in external magnetic fields
between 0 and 70 kOe. The substitution of Al for Mg leads to a substantial
reduction of the heat transport via electronic quasiparticles. The analysis of
the K(T,H) data implies that the Al impurities provoke an enhancement of the
intraband scattering rate, almost equal in magnitude for both the sigma- and
the pi band of electronic excitations. This is in contrast with conclusions
drawn from analogous data sets for material in which carbon replaces boron and
where mainly the intraband scattering rate of the sigma band is enhanced. Our
complete data set, including additional results of measurements of the
low-temperature thermal conductivity of pure MgB2, confirms the validity of the
Wiedemann-Franz law for both pure and doped MgB2.
