Why are piano-type hinges prime spots for corrosion?

The correct answer highlights the issue of dissimilar metals, specifically the combination of steel and aluminum in piano-type hinges. When two different metals come into contact, especially in the presence of moisture, galvanic corrosion can occur. This is a type of electrochemical reaction where the more active metal (in this case, aluminum) tends to corrode faster than it would alone, while the less active metal (steel) may corrode more slowly, but is still involved in the process.

Dissimilar metal combinations expand the risk of corruption because the protective oxide layer on aluminum can get disrupted, exposing unprotected areas to corrosion. This is especially pronounced in environments where there is moisture, which may sit in the hinge and promote corrosion further. Such hinges must be monitored regularly for wear and corrosion to maintain their integrity, especially in aviation applications where failure could have severe consequences.

The other options do not accurately address the core reason for corrosion in these hinges. Non-corrosive materials and heavy lubrication might mitigate some erosion but do not prevent corrosion stemming from dissimilar metals. Additionally, it's inaccurate to suggest that these hinges are not exposed to moisture; they often are, particularly on aircraft exposed to various weather conditions.