Al+Cl2= what is the chemical reaction?

Normally aluminium is a very reactive metal, once it expose in the air, there is a layer of aluminium oxide formed which is resistant to anything.

I am not sure do you have an aluminium metal(pure or have an oxide form on the outer layer) and chlorine gas, but if you want to produce Aluminium chloride, then here is the condition you need to have for the reaction:

Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between 650 to 750 °C.[4]

2 Al + 3 Cl2 → 2 AlCl3
2 Al + 6 HCl → 2 AlCl3 + 3 H2
In the US in 1993, approximately 21,000 tons were produced, not counting the amounts consumed in the production of aluminium.[6]

Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid. Heating this solid does not produce anhydrous aluminium trichloride, the hexahydrate decomposes to aluminium oxide when heated to 300 °C:[6]

2 AlCl3 + 3 H2O → Al2O3 + 6 HCl
Aluminium also forms a lower chloride, aluminium(I) chloride (AlCl), but this is very unstable and only known in the vapor phase

You have aluminium and you have chlorine what do you guess they might react to? Aluminium chloride? Look up Aluminium Chloride on wikipedia and see if that's possible. It actually gives you the full balanced equation but let's pretend it doesn't so we can balance it.

Al + Cl2 > AlCl3

now to balance it, just make sure the same number of atoms on the right of the equation is the same number of atoms on the left.

2Al + 3 Cl2 > 2 AlCl3

Hope this helps.

2AL + 3Cl2--> 2AlCl3