ELI5: This is elemental aluminum and bromine reacting together. They form strong bonds with each other forming Aluminum Bromide. It is an exothermic reaction so some of the unreacted bromine is vaporized throwing off orange smoke and because it is so exothermic the aluminum gets hot enough to melt and spark. Aluminum bromide is hygroscopic (absorbs water from the air) which make it fume in air, forming a white cloud. Aluminum bromide reacts violently with water to produce HBr and aluminum hydroxide or oxide which are both toxic and can cause burns. Bromine is a strong oxidizing agent and is also toxic.

Science: First off as always the balanced chemical equation 2 Al(s) + 3 Br2(l) → 2 AlBr3(s)

Al's electronegativity is 1.5 and Br is 2.8. This is a difference of 1.3 for the Al-Br bond. This means it forms a strong polar covalent bond Aluminum has a Pauling electronegativity of 1.5 and bromine has an electronegativity of 2.8. The resulting electronegativity difference of 1.3 for the aluminum-bromine bond falls well within the commonly accepted range for polar covalent bonds