a)Conventional welding techniques are not normally used to join aluminium superstructures to steel hulls because of the different properties of the two metals. Steel has a higher melting point than aluminium, so when the two metals are welded together, the aluminium can melt before the steel, resulting in a weak joint. Additionally, steel is more prone to rust than aluminium, and the heat from welding can accelerate the corrosion process.
b)The particular problems associated with an aluminium superstructure bonded to a steel hull include:
Galvanic corrosion: This type of corrosion occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte (such as seawater). The electricity from the steel hull can flow to the aluminium superstructure, causing the aluminium to corrode.
Stress corrosion cracking: This type of cracking can occur in aluminium alloys that are subjected to stress and a corrosive environment. The stress can come from the weight of the superstructure, or from the waves and wind.
Fatigue: Aluminium is more susceptible to fatigue than steel, so the superstructure is more likely to crack under repeated loading.
c)The maintenance that should be carried out to ensure the continued structural integrity of the vessel includes:
A typical transition joint that could be used to attach an aluminium superstructure to a steel hull is a bolted joint. Bolted joints are strong and can be easily inspected and maintained. They also help to isolate the two metals from each other, which can reduce the risk of galvanic corrosion.
d)? appears to be missing :/