Answer:
When aluminum is added to cold dilute hydrochloric acid, there is no reaction because aluminum is a highly reactive metal, but it is protected by a thin oxide layer on its surface. This oxide layer is not easily dissolved by dilute hydrochloric acid, so the aluminum does not react with the acid. In order to react with the acid, a stronger acid such as sulfuric acid or nitric acid is needed to dissolve the oxide layer. Additionally, a higher concentration of hydrochloric acid is also needed to react with aluminum.
Another possible reason is that Aluminium metal react with hydrochloric acid to produce hydrogen gas and aluminum chloride salt, but the reaction is relatively slow and requires heat to speed it up. In cold dilute hydrochloric acid, the reaction rate is too slow to observe any visible change.