Engine materials — aluminium alloys are widely used for cylinder blocks primarily because:

Introduction / Context:
Choice of material for engine blocks affects mass, thermal management, noise, vibration, and manufacturing cost. Historically many blocks were cast iron, but aluminium alloys are common in modern gasoline engines because of their advantages in weight and heat transfer. This question asks for the primary reason aluminium is chosen for blocks in many applications.

Given Data / Assumptions:

• Comparison between aluminium alloys and cast iron as typical block materials.
• Performance priorities include weight reduction and thermal management.
• Manufacturing options include cast-in liners, parent bore coatings, or inserted sleeves.

Concept / Approach:

Aluminium has a much lower density than cast iron, significantly reducing vehicle mass and improving fuel economy and handling. It also has higher thermal conductivity, aiding heat rejection from cylinder walls and allowing faster warm-up and improved knock control. While cost and liner requirements vary by design, the fundamental drivers are weight and heat dissipation. Aluminium blocks often use cast iron liners or advanced surface treatments; the absence of liners is not guaranteed and is not the reason for choosing aluminium. Matching piston material to block material is a secondary design consideration, not the primary justification for the block material itself.

Step-by-Step Solution:

Verification / Alternative check:

Automotive engineering references and OEM designs consistently cite mass reduction and thermal conductivity as the rationale for aluminium blocks, with specific liner strategies selected per application.

Why Other Options Are Wrong:

Material cost is low — Aluminium alloy castings are often more expensive than grey iron for equivalent strength.
Does not require any cylinder liners — Many aluminium blocks do use liners or coatings; not universally true.
Piston is also aluminium — Common, but piston material does not dictate block material choice.

Common Pitfalls:

Assuming aluminium blocks never need liners; ignoring trade-offs such as stiffness and wear resistance managed by design features.

Final Answer:

it is lighter and have good heat dissipation characteristics