Corrosion behaviour of brazing material AA4343

This paper is part of a work devoted to corrosion of brazed AA4343/AA3003/AA4343 materials on water side of automotive heater cores. The microstructure of the superficial resolidified AA4343 brazing material has been previously characterised [1] and [2]. It is composed of large (Al) grains separated by valleys containing multiphase deposits of (Al), Si and α-Al(Mn,Fe)Si. The present study focuses on its electrochemical behaviours in neutral water–ethylene glycol mixtures at different temperatures with and without chloride ions. Three types of behaviour are revealed: (i) passivation, (ii) defective passivation and (iii) pitting corrosion at the corrosion potential. The defective passivation is investigated in greater depth. The results show that Si needles do not participate in the corrosion progress whereas the α-Al(Mn,Fe)Si particles are preferential sites for corrosion attacks. α-Al(Mn,Fe)Si particle/matrix interactions are responsible of the defective passivation at valleys level where the α-Al(Mn,Fe)Si phase particles are mainly concentrated. Increasing the temperature enhances this reactivity whereas addition of ethylene glycol decreases it and favours a transition from defective passivation to passivation for ethylene glycol content higher than 55%

Corrosion behaviour of brazed multilayer material AA4343/AA3003/AA4343: Influence of coolant parameters

This paper is the second part of a work devoted to corrosion in brazed AA4343/AA3003/AA4343 materials on the water side of automotive heater cores. In the first part of the study [S. Tierce, N.Pébère, C. Blanc, C. Casenave, G. Mankowski, H. Robidou, Electrochim. Acta 52 (2006) 1092], corrosion initiation in the surface layer (i.e. the residual cladding) has been investigated. It has been associated to defective sites in the passive film covering the alloy. The defective sites are linked to a-Al(Mn,Fe)Si particles built up during brazing process. Interactions between a-Al(Mn,Fe)Si particles and the matrix are responsible for the observed behaviour. The present study focuses on the propagation of corrosion through the material in neutral water–ethylene glycol mixtures with and without chlorides. Comparison of the electrochemical behaviour of the three layers of the brazed material (i.e. the residual cladding, the "band of dense precipitates (BDP)" and the core material) revealed that the residual cladding was nobler than the BDP and the core material and thus that the corrosion should propagate through the inner layers due to galvanic coupling: the inner layers constitute the anode and the residual cladding the cathode. Increasing the ethylene glycol content in the water–ethylene glycol mixture decreased the rate of consumption of the materials whereas addition of chloride ions increased it. Mass variation measurements of brazed material in different solutions containing the degradation products of ethylene glycol showed that only glycolate ions had a slight detrimental effect. Corrosion tests performed in heater core tubes allowed the propagation mechanisms to be confirmed

Study of the microstructure resulting from brazed aluminium materials used in heat exchangers

Re-solidification of AA4343 cladding after brazing as well as the related precipitation in the modified AA3003 core material have been investigated. Analysis of the re-solidified material showed that partial dissolution of the core alloy occurs in both the brazing joints and away of them. Far from the brazing joints, the dissolution is, however, limited and diffusion of silicon from the liquid into the core material leads to solid-state precipitation in the so-called “band of dense precipitates” (BDP). On the contrary, the dissolution is enhanced in the brazing joint to such an extent that no BDP could be observed. The intermetallic phases present in the resolidified areas as well as in the core material have been analyzed and found to be mainly cubic alpha-Al(Mn,Fe)Si. These results were then compared to predictions made with available phase diagram information

The Race to Regional Hegemony: A Case Study of the Iran-Saudi Rivalry in Yemen

The main goal for this thesis is to review how the Islamic Republic of Iran and the Kingdom of Saudi Arabia’s actions in Yemen’s civil war can be explained through the international relations theory Classical Realism. Studying Iran and Saudi Arabia’s rivalry is important for academic study because it creates an imbalance of power in the Middle East and intensifies security issues in the region. Both Iran and Saudi Arabia hold the most influential economic and political systems in the Middle East, presenting a dilemma for power and security between the two. There most recent example of this rivalry can be seen through their engagement in the Yemeni civil war. By invading the state sovereignty of Yemen to conduct a proxy war, Iran and Saudi Arabia have exemplified their desire to obtain regional hegemony. In this paper, I will utilize the zero-sum game and security dilemma, to explain Iran and Saudi Arabia’s motivations and participation in the Yemeni civil war. Furthermore, I will argue that Iran and Saudi Arabia are utilizing Yemen to obtain geostrategic power in their race towards regional hegemony

Etude de la corrosion des alliages d'aluminium brasés constituant les échangeurs thermiques utilisés dans les véhicules automobiles

La représentativité des tests de corrosion est un sujet récurrent dans les études de durabilité des matériaux. Le travail s’est intéressé aux alliages d’aluminium brasés AA4343/AA3003 /AA4343 utilisés pour la fabrication des échangeurs thermiques automobiles. Leur structure métallurgique et leurs mécanismes de dégradation en corrosion ont été étudiés. L’étape d’initiation dans le placage resolidifié a été associée à des interactions entre les particules de phase ®¡Al(Mn; Fe)Si et l’aluminium. Un couplage galvanique entre la couche noble que constitue le placage résiduel et le matériau de cœur induit ensuite une propagation caverneuse. L’influence de la composition de l’électrolyte et de la température a été évaluée. L’utilisation d’un antigel dégradé synthétique à pH neutre, contenant 10 % d’éthylène glycol, des chlorures (354 ppm) et des glycolates (500 ppm) permet d’obtenir des faciès de corrosion comparables à ceux générés en service. ABSTRACT : The representativity of corrosion testing is a recurrent topic in studies of material durability. This work was devoted to brazed aluminium alloys AA4343/AA3003/AA4343 used for automotive heat exchangers. The metallurgical structure and the mechanisms of corrosion degradation were investigated. The initiation of the corrosion in the resolidified cladding was associated to ®¡Al(Mn; Fe)Si phase particles / (Al) matrix interactions. Then, a galvanic coupling between the noble layer constituted by the residual cladding and the core material was found to induce cavernous propagation of the corrosion. The influence of electrolyte composition and temperature was investigated. The use of a synthetic degraded coolant at neutral pH, containing 10 percent ethylene glycol, chloride (354 ppm) and glycolate (500 ppm) allows corrosion features comparable to those generated in service to be obtained

Eggs, small beer, and Hardy : The poetry and prose of Philip Larkin

The bleak sense of failure and dissatisfaction that appears to infest Philip Larkin\u27s poetry is caused not only by the twentieth-century writer\u27s usual distrust of God, or nature, or humanity, but it is also the direct result of his recognition of the limitations of art, a recognition that helps to explain his decision in 1982 to stop writing poetry altogether. He did, however, spend forty years producing poems in which he tries to preserve things he has seen, thought, or felt. Since he insists on describing commonplace events and ordinary people and refuses to over-romanticize the realistic sights and occurrences on which he bases his work, it is easy to see why he would reject Yeats and embrace Hardy as his poetic master. However, even though his poems do generally begin with a factual description using specific details, they usually culminate in a closer examination stating the importance of these details in a more universal context. He, therefore, tends to build up to a big finish--oftentimes to a metaphorical flourish. Larkin not only insists on commonplace subject matter, but he also attempts to return poetry back to average or common readers. He thinks poetry should and must compete with the local pub and with the television set. He consequently rejects modernism, blaming Pound and Eliot for making poetry too obscure for the average reader to understand. Since he views modernism as being overly cold, sterile, and intellectual, he tries to remake poetry into a vehicle for emotions capable of giving pleasure to any reader. He, therefore, insists that poetry must deal with human emotions as well as the intellect and tries to make reading poetry a pleasurable experience once again. However, even though he attempts to establish a realistic, empirical, photograph-like effect, many of his poems reflect his awareness that such an art is artificial at best and impossible at worst. Not only does he doubt the intrinsic value of art, but he also ultimately rejects all capital-t Truths. God, nature, art, and love are all questioned and eventually devalued. All an artist can hope to accomplish is an appropriate falsehood ; Truths are out of the question