Investigation of temperature effect on mechanical properties of steel-aluminium transition joint used in ship construction

Aluminum materials are used in ship building for decrease weight, increasing day by day. Aluminum is using generally all areas of ship hull about cost and strength. Generally, when ship hull constructıon is built from steel material, superstructures is built from aluminum material. Because of this, the total weight of ship decreases, weight of steel hull construction decreases and ship stability (balance status) increases. It is more economical, in case of aluminum and steel are using as Hybrid materials. Using of aluminum alloy parts in ships; requires safe, efficient and economical welding technologies. There are some difficulties because of physical and metallurgical important differences between welding of these different metals. One of the easiest and most effective ways to overcome these challenges is to use transfer joints. Transition joints are bimetal strip or pads that are using for facilitate joint welding of different metals. Especially they are using on areas where not possible to joint different metals each other with traditional welding. There is some restriction using of Transition Joints. Providing the desired values of joint Strength and providing resume service life of constructıon integrity, the Transition Joint welding must be done according to the rules. In the case of non-compliance with the rules interfaces will be exposed to excessive heat, the strength of the material will decrease. In the experiments; Main Metal D Grade Steel, Coated Metal EN AW 5083 series aluminum and intermediate layer is EN AW 1050 series aluminum were used. Ram test materials according to MIL-J-24445A standard and ABS standards are prepared and tensile strength of sample was examined about several times and several heat degrees. Decreasing of tensile strength above 300 ˚C is detected, about serious ratio. At the same degree, when the duration is increased, the strength values is decreased. In the second part of this work, reasons of decreasing tensile strength are examined. Increasing of aluminum steel interface hardness measurements and micro building examines were completed. When the increasing of heat and time, steel-aluminum interface hardness measurements is increasing and microstructures detected in the interface. Providing intended joint and strength features Transition Joint, welding process requires extreme care. Providing decreasing of Transition Joint strength there is some considerations and recommendations; • The heat between aluminum and steel interface must be under 300 ˚C (570 ˚F). • Excessive and thick welding must be avoided. • Multiple thin weld must be preferred instead of a thick weld. • Short and rapidly welding method must be preferred instead of continued long welding. • Practically, Transition joint must be welded on aluminum part, firstly. Because of this, while Transition joint is welded on the steel part, heat decrement will be better. • It must be avoided, welding close from 3 mm to each side. • It is advisable to showing the interface temperature using a heat-sensitive paint or other suitable methods, until the welder has enough experience. • The welding parameters must be provided cooling time between passes in order to ensure full penetration of the welding seam.