\usepackage{float}
\floatplacement{figure}{htbp} % here, top, bottom, extra-page
%\floatstyle{boxed}
%\restylefloat{figure}


\usepackage{caption}
\captionsetup[figure]{name=Schéma}

\let\legacyFigure\figure
\let\endlegacyFigure\endfigure

\renewenvironment{figure}{%
  \begin{legacyFigure}%
    \begin{mdframed}[linecolor=gray]%
}{%
  \end{mdframed}%
  \end{legacyFigure}%
}