For a 5" x 6" water pump impeller with a 6" inlet and 5" outlet made of aluminium, here are some considerations:

1. Aluminium Material: Aluminium impellers are lightweight, making them suitable for applications where weight is a concern. They offer reasonable corrosion resistance but may not be as durable as other materials like cast iron or stainless steel. However, for applications where weight is a critical factor or where corrosion is not a significant concern, aluminium impellers can be a suitable choice.

2. Impeller Size: The 5" x 6" dimensions refer to the size of the impeller, indicating a 5-inch inlet and 6-inch outlet. It's essential to ensure that the impeller size matches the pump housing and other components to ensure efficient pumping performance.

3. Operating Conditions: Consider the specific operating conditions of your application, such as the type of fluid being pumped, temperature, pressure, and the presence of any abrasives or solids. Aluminium impellers may be suitable for applications with relatively clean water and moderate operating conditions.

4. Application Suitability: Evaluate whether an aluminium impeller is suitable for your specific application requirements. While aluminium impellers offer advantages in terms of weight and cost, they may not be appropriate for applications with highly corrosive fluids or extreme operating conditions.

Before selecting an aluminium impeller for your water pump, ensure that it meets the requirements of your application and consult with a pump manufacturer or supplier for expert advice.