bold math in section

\documentclass{article}

\makeatletter
\g@addto@macro\bfseries{\boldmath}
\makeatother

\usepackage[pdfstartview={FitH},
            pdfencoding={auto},
            bookmarksopen={true}]{hyperref}

\begin{document}
\title{\bf This is $a+b=\alpha+\beta$ article title}
\author{Test $a+b=\alpha+\beta$}
\maketitle

\tableofcontents

\section{Bold math test \texorpdfstring{$a+b=\alpha+\beta$}{a+b=α +β }}
\end{document}