The aluminium industry supplies various car body sheet qualities tailor-made to meet the requircmcnts of the car producers. The most important alloy types are AlMgSi (free from stretcher-strain markings after forming and hence suited for outer skin) and AlMg (for interior use). I n addition t o the significant weight savings it is its long service life which makes aluminium an attractive alternative to steel sheets. A prerequisite for good corrosion resistance is a surface treatment optimised for aluminium. This includes t h e creation of a phosphate surface layer t o allow lacquer coating together with steel and galvanized steel o n existing lines.The Accelerated Outdoor ExposurcTest (VDA (121-414) proved to be the only static corrosion test mcthod suitable for assessing the resistance level of thc final lacquered car body. In addition t o the proper selection of alloy and surface finishing tcchnique it is important that some aluminium-specific precautions are taken during manufacture if the full long service potential of the material is to be realized.

No abstract

Test blankets of a thermo-nuclear fusion reactor are subjected during service to alternating thermal and mechanical stresses as a consequence of the pulsed reactor operation. Of particular concern is the thermo-mechanical fatigue (TMF) endurance of 9% Cr low activation ferrite-martensite steels. To design such blankets operating under the above loading conditions, for the time being fatigue life is predicted using design codes based on isothermal fatigue material data, but these codes will be verified with TMF data. Within the European Materials Long Term Programme for fusion research several laboratories are involved in performing TMF experiments using different facilities and samples. Results of a TMF-round robin of four European laboratories will be reported. Comparison of the various test data obtained will give a better understanding for these kinds of tests and enable an in-depth discussion of the scatter of the results, of its reason and what the implications are in terms of a TMF standard.

Two different modes of coating crack initiation are observed in an aluminide coated single crystal nickel base alloy upon thermomechanical fatigue loading with a cycle where the lag of the strain cycle behind the temperature cycle was 135‡. Minimum and maximum cycle temperatures were 300‡C and 1050‡C, respectively. At applied mechanical strain ranges in excess of 0.8% the coating fails in a brittle manner, initiating a network of nearly equidistant parallel cracks. As opposed to this line initiation mode, a point initiation mode of multiple thumbnail crack origins is found for low strain ranges. Uncoated test specimens fail by point initiation at all strain ranges. The line initiation behaviour can be rationalized using a fracture mechanics approach based on energy release rate concepts to estimate the strain (or stress) to first coating crack and to predict the coating crack density during the test. This model highlights the effects of various parameters, such as coating thickness and temperature, on the failure mode. The influence of the ductile-brittle transition temperature and the stress-temperature coupling on the failure mode of the coating is discussed and the model predictions are compared with the experimental observations.

Thermo-mechanical fatigue of nickel-base superalloys has been carried out for more than twenty years, but a unified standard for such tests has yet to be fully formulated. As a consequence of this, even excluding differences in testing procedure from laboratory to laboratory, the range of testing conditions in use is very large. In this paper, the authors consider the effect of the different parameters in a TMF test such as hold-time and temperature-mechanical phase angle on the thermo-mechanical response of test samples. This is carried out in terms of both stress response and sample life, in order to identify the common trends in the sample damage during the evolution of the mechanical response. To date, no definitive test program systematically covering the different variables has been published in the scientific literature. As, even after a long span of time, the literature data for many alloys is sparse, the work presented here concentrates on analyzing TMF response data from test programs carried out by the authors on the single crystal nickel-base alloy SRR99. [S0094-4289(00)01003-3]