In this paper, we study the supports of measures in the free additive convolution semigroup $\{μ^{\boxplus t}:t>1\}$, where $μ$ is a Borel probability measure on $\mathbb{R}$. We give a formula for the density of the absolutely continuous part of $μ^{\boxplus t}$ and use this formula to obtain certain regularizing properties of $μ^{\boxplus t}$. We show that the number $n(t)$ of the components in the support of $μ^{\boxplus t}$ is a decreasing function of $t$ and give equivalent conditions so that $n(t)=1$ for sufficiently large $t$. Moreover, a measure $μ$ so that $μ^{\boxplus t}$ has infinitely many components in the support for all $t>1$ is given.

21 pages