  In present work, we systematically study the $\alpha$ decay half-lives of 170
even-even nuclei with $60 \leqslant Z \leqslant 118$ within the two-potential
approach while the $\alpha$ decay preformation factor $P_\alpha$ is obtained by
the cluster-formation model. The calculated results can well reproduce the
experimental data. In addition, we extend this model to predict the $\alpha$
decay half-lives of 64 even-even nuclei with $104 \leqslant Z \leqslant 128$
whose $\alpha$ decay is energetically allowed or observed but not yet
quantified. For comparing, the two famous models i.e. SemFIS proposed by D.
Poenaru ${et\ al.}$ [\href
{https://doi.org/10.1209/0295-5075/77/62001}{Europhys. Lett. \textbf{77} (2007)
62001}] and UDL proposed by C. Qi ${et\ al.}$ [\href
{https://doi.org/10.1103/PhysRevLett.103.072501}{Phys. Rev. Lett. \textbf{103}
(2009) 072501}] are used. The predicted results of these models are basically
consistent. At the same time, through analyzing the changing trend of $\alpha$
decay energy $Q_{\alpha}$ of \emph{Z} = 118, 120, 122, 124, 126 and 128
isotopes nuclei with the increasing of neutron number \emph{N} and that of
$\alpha$ decay preformation factor $P_\alpha$ of those isotopes even-even
nuclei with the increasing of neutron number \emph{N}, \emph{N} = 178 may be a
new neutron magic number.
