Investigation of Hot Cracking Phenomena in Fusion Welding of High-Strength Aluminum Alloys and the Effect of Friction Stir Processing (FSP) Pre-Treatment on the Weldability of 7075 Aluminum Alloy

, M.Sc. Thesis Sharif University of Technology Pirjamadi, Alireza (Author) ; Pouranvari, Majid (Supervisor) ; Movahedi, Mojtaba (Supervisor)

Abstract

High-strength aluminum alloys are widely used in various industries; however, their usage is limited to solid-state welding or mechanical joints due to their low weldability. The main metallurgical challenge of alloy 7075 welding is hot cracking. Thus, the mentioned alloy is introduced as a "non-weldable alloys" category. In this study, the PMZ was investigated, and it was shown that precipitations play an essential role in intensifying the phenomenon of partial melting. On the other hand, the result of the mechanisms activated in the PMZ, called the "L" region, occurs in the grain boundaries during welding. Welded plate with FM1050 causes liquation cracking, while Welded plate with FM4043...

Investigation on the Effect of Friction Stir Processing on the Fusion Weldability of Magnesium Alloys

, M.Sc. Thesis Sharif University of Technology Jiryaei Sharahi, Hassan (Author) ; Pouranvari, Majid (Supervisor) ; Movahedi, Mojtaba (Supervisor)

Abstract

Magnesium alloys, as the lightest structural alloys having a density of about one-fourth that of steels, offer significant potential for improving the energy efficiency of various transportation systems. Welding is a critical enabling manufacturing technology; therefore, the widespread application of a material is highly influenced by their weldability. Liquation and Liquation cracking are crucial weldability issues for fusion welding of cast AZ91 Mg alloy. The constitutional liquation of the coarse eutectic Mg17Al12 intermetallic phase is responsible for the occurrence of liquation cracking during fusion welding of this alloy. Here, friction stir processing (FSP) treatment, a successful...

Prediction of Weld Solidification Cracking Susceptibility in Dissimilar Aluminium Alloy Joints

, Ph.D. Dissertation Sharif University of Technology Bodaghi, Fatemeh (Author) ; Kokabi, Amir Hossein (Supervisor) ; Movahhedi, Mojtaba (Supervisor) ; Tavakkoli, Rouhollah (Co-Supervisor)

Abstract

Solidification cracking is one of the most common types of cracks in aluminum alloy welds. Predicting the possibility of Solidification cracking can be useful in selecting the variables of the welding process in such a way that a crack-free joint is obtained. In the present research, in the first stage, a criterion of sensitivity to solidification cracking is presented by considering the anisotropic permeability equation and direction of applying deformation to the melt pool. Then, the criterion has been investigated for aluminum-copper and aluminum-copper-silicon alloys. The results indicated that Al-3.5 wt% Cu alloy has the highest solidification cracking susceptibility (SCS) in the...

Fusion Welding of Dissolvable Magnesium Alloy

, M.Sc. Thesis Sharif University of Technology Salehi, Mohammad (Author) ; Movahedi, Mojtaba (Supervisor)

Abstract

Magnesium alloys as the lightest structural alloys, have a strong potential for improving the energy efficiency of different transportation systems such as automobiles, aerospace and electronics due to their high strength to weight ratio. Welding plays a crucial role as a foundational manufacturing technology. Hence, the extensive utilization of materials is greatly impacted by their ability to be welded.These alloys are highly susceptible to hot cracking such as liquation cracking during the fusion welding processes.Various mechanisms play a role in the occurrence of hot cracking, but the constitutional liquation of the coarse eutectic mg17al12 intermetallic phase is accountable for the...