F.A. Darwish

Bio: F.A. Darwish is an academic researcher from The Catholic University of America. The author has contributed to research in topics: Ultimate tensile strength & Charpy impact test. The author has an hindex of 2, co-authored 3 publications receiving 29 citations.

Effect of weld metal microstructure on the monotonic and cyclic mechanical behavior of tig welded 2091 Al–Li alloy joints

Abstract: The effect of TIG welding on the mechanical behavior of Al–Li alloy 2091-T851 has been investigated by means of tensile and fatigue testing. Compared to the base alloy, as-welded joints were found to display significant reductions in both tensile and fatigue strengths and to suffer a drastic degradation in ductility. Such behavior is primarily related to the presence of large elongated R phase precipitates at the weld metal grain boundaries, which leads to intergranular crack propagation through that part of the joint. Substantial microstructural changes, though, can be induced in the weld metal by subjecting the welded joints to a post-weld T6 type heat treatment. This promotes dissolution of the R phase, thus enhancing the tensile properties as well as the fatigue strength, consistent with the predominance of transgranular fracture of the weld metal in the heat treated joints. Finally, the microstructural aspects presented above indicate that the weld metal is plastically more heterogeneous than the base alloy and therefore is expected to work-harden faster, which is borne out by the tensile test results.

On the tempered martensite embrittlement in AISI 4140 low alloy steel

Abstract: In the present investigation the Auger electron spectroscopy (AES) technique was used to determine local carbon and phosphorus concentrations on the fracture surfaces of as-quenched and quenched-and-tempered (at 350°C) AISI 4140 steel specimens austenitized at low and high temperatures. The AES results were rationalized to conclude that, although carbride growth as well as phosphorus segregation are expected to contribute to tempered martensite embrittlement, carbide precipitation on prior austenite grain boundaries during tempering is seen to be the microstructural change directly responsible for the occurrence of the referred embrittlement phenomenon.

Influence of notch root radius on the fracture behavior of aisi 4140 steel austenitized at low and high temperatures

Abstract: A study has been made of the influence of notch root radius on the ambient temperature toughness of commercial AISI 4140 steel austenitized at 870 and 1200°C and tested in the as-quenched and quenched and tempered at 200 and 350°C conditions. Charpy specimens containing V-notches of different root radii were loaded to failure in three point slow bending. Toughness values were calculated and the specimens were fractographically examined. The results obtained are seen to confirm the concept of characteristic distance for failure as well as its validity to appropriately explain differences encountered in plane strain fracture toughness. The results also show that low temperature austenitizing invariably gives rise to superior rounded notch toughness as compared to high temperature austenitizing treatment. This observation is found to be associated with shear lip formation along the notch root for conventionally austenitized specimens. Shear lip width is seen to increase with the notch radius and with the tensile ductility of the material.

Effect of laser beam welding on tear toughness of a 1420 aluminum alloy thin sheet

Abstract: A tear test has been conducted for a 1420 Al–Li alloy thin sheet and its laser welded joint. The test was based on the ASTM B 871-01, standard test method for tear testing of aluminum alloy products. Moreover, the hardness distribution and microstructure of the alloy and welded joints were investigated. The test results indicate that there exists slight orientation dependence of tear energies for the L–T and T–L base metal. In addition initiation energies are higher than the propagation energies for all the tear test specimens, and the tear energies of base metal are higher than those of weld metal and HAZ. Thus, it is considered that the tear toughness of the laser-welded joints is obviously decreased for the 1420 Al–Li alloy thin sheet. Fracture surface shows strong delamination structure for the base metal. Moreover, there exists a feature of fracture along grains or subgrains for the weld metal. Thus, the obvious decrease in tear toughness of weld metal is due to the transition of fracture mode from transgranular to intergranular.

Study on Pores in Ultrasonic‐Assisted TIG Weld of Aluminum Alloy

Abstract: Ultrasonic‐assisted tungsten inert gas welding was carried out on a thin plate of 2195 Al‐Li alloy, and the characteristics of the weld pores were analyzed in terms of their size and porosity. The effects of welding speed and ultrasonic power on the porosity and size of the pores were investigated. The pores were found to occur primarily adjacent to the surface of the weld. The porosity decreased and the size increased with a decrease in welding speed. The effect of ultrasonic power on the characteristics of the pores was different from that of the welding speed. The porosity and size of the pores decreased and then increased with an increase in ultrasonic power. A relationship was found between the transient cavitation intensity and the characteristics of pores. An increasing transient cavitation intensity results in a decrease in the porosity and size of pores when the transient cavitation intensity is lower. However, it can result in an increase in the porosity and pore size when the transient cavitation intensity further increases. Finally, the influencing mechanism of cavitation on welding pores was discussed.