Victor H. López

Wettability of TiC by commercial aluminum alloys

The effect of alloying elements on the wettability of TiC by commercial aluminum alloys (1010, 2024, 6061 and 7075) was investigated at 900°C using a sessile drop technique. Wetting increased in the order 6061 < 7075 < 2024 < 1010 for both, static argon or vacuum atmospheres. Alloys 1010 and 2024 wet TiC under both atmospheres, leading to contact angles in the order of 60° and less, while 7075 only wets under vacuum, with the poorest wettability being exhibited by 6061. Evaporation of Zn and Mg under vacuum conditions contributed to the rupture of the oxide film covering the aluminum drop and thereby improving wetting and spreading. Continuous and isolate Al4C3 was detected in all the cases. CuAl2 precipitation at the interface slightly decreased Al4C3 formation and increased the adhesion of 2024 to TiC.

A comparative study of the MIG welding of AI/TiC composites using direct and indirect electric arc processes

Metal inert gas welding of Al-1010/TiC/50p composites was carried out on 9 mm thick square bars by applying the electric arc directly and indirectly. Three pre-heating temperatures were used, 50, 100 and 150°C but only direct electric arc (DEA) was applied at room temperature. Welds were microstructurally examined and tested under tensile load. Complete penetration was achieved using both DEA and IEA methods. Uniform welds were obtained using indirect electric arc (IEA), meanwhile broadening was observed in the upper part in DEA welds facilitated by mixture of the base material with the filler. Microstructural observations showed good lateral fusion of the parent composites, little or no dissolution of TiC by IEA and only slight dissolution by DEA, which led to TiAlx formation during solidification. The presence of Al4C3 was not detected. Microhardness weld profiles revealed that the use of IEA reduces the heat affected zone (HAZ). Mechanical failure of the samples was consistently in the weld zone. Mechanical strength in IEA welds (182–186 MPa) was consistent irrespective of the pre-heating conditions and dependant only of the consumable (Al-2024). The mechanical strength of DEA welds was affected to some extent by the incorporation of the reinforcing particles into the weld region and wettability aspects inherent to the welding conditions. The use of IEA seems to be a suitable route for joining Al-based composites even when the reinforcement content is high.

Effect of the weld thermal cycles of the modified indirect electric arc on the mechanical properties of the AA6061-T6 alloy

Results of temperature measurements during welding of 12.7 mm thick AA6061-T6 alloy plates by modified indirect electric arc (MIEA) are presented. This study describes the thermal cycles in the heat-affected zone (HAZ) and also in the fusion zone. Depending upon the position of the transducers, the maximum temperatures measured in the HAZ ranged from 308 to 693°C, these measurements were related with the tensile test results and the failure zone reported previously by the authors (Ambriz et al., S&I 2006;11:10–17). It was observed that there is a decrease in the mechanical strength of the welded joints, due to the microstructural changes undergone by the AA6061-T6 alloy in which formation of the β′ occurs according to the time–temperature transformation diagram. The inherent cooling conditions of the weld pool observed for the MIEA technique (single welding pass) have made it possible to establish the characteristics of solidification and microstructure for a specific cooling rate.

Spreading Mechanism of Molten Al-Alloys on TiC Substrates

The contact angle data drawn from sessile drop tests of commercial aluminum alloys (1010, 2024, 6061 and 7075) on TiC substrates (at 900 °C, under vacuum and argon atmospheres) was plotted on a logarithmic time scale. Several aspects were taken into account to describe the spreading mechanism in four kinetic stages in systems that exhibited wetting (1010, 2024 in both environments and 7075 under vacuum). It was found that commercial multi-element alloys do not improve wetting of Al on TiC and that alloying elements and the atmosphere exert a significant role on the wetting behavior in the early stages. A physical model describing spreading in the early stages is presented. The influence of alloying elements and the type of atmosphere on the deoxidation of the drops are discussed.

ACPD detection and evaluation of 475 °C embrittlement of aged 2507 super duplex stainless steels

An investigation to evaluate embrittlement of thermally aged 2507 super duplex stainless steel (SDSS) by means of an accurate measurement of the electric conductivity using an alternating current potential drop (ACPD) probe is conducted. Samples were aged for different periods up to 300 h at 475 °C. Results obtained from the ACPD measurements show appreciable increases in electric conductivity of samples with prolonged exposure to this temperature. In addition, the hardness of the samples increases significantly for long holding times, resulting in an embrittlement of the SDSS. These results are also supported by other data from sample-based laboratory techniques, i.e. microhardness and microscopy results which provide more direct evidences of the sensitization. This paper, therefore, demonstrates the feasibility of using the ACPD probe in field applications.

Effect of the Perpendicular Electromagnetic Field in the 304 Austenitic Stainless Steel Welding in a Single Pass

Plates, 12.7 mm thick, of AISI 304 austenitic stainless steel were welded using a non-conventional joint design in a single pass with and without the application of magnetic fields with different orientations. A perpendicular electromagnetic field was applied in order to obtain high penetration by turning helicoidally the path of the plasma within the groove of the joint during welding. Observation of the transverse profiles of the welds revealed fully penetrated welds; however, lack of sidewalls fusion was seen in every profile. Welding with magnetic field decreased the extent of this defect. The effect of the magnetic field was evaluated in terms of susceptibility to localized corrosion in the heat affected zone (HAZ) by the double loop-electrochemical potentiokinetic reactivation (DL-EPR) test. These results indicated that the as-received plates were already sensitized and plain welding worsened this condition in the HAZ. DL-EPR curves revealed that welding with perpendicular magnetic field reduced the degree of sensitization in the HAZ. Examination of the essayed surfaces in the scanning electron microscope (SEM) showed that generalized corrosion took place instead of localized corrosion.

Mechanical Evaluation of IN718-AL6XN Dissimilar Weldment

Gas tungsten arc welding (GTAW) was used to join Inconel 718 and AL6XN plates. The welding was made in aged condition for the Inconel 718 plates. Mechanical properties were determined by tensile, microhardness and instrumented Charpy impact tests. An ERNiFeCr-2 filler metal was fed by a semiautomatic mechanism. The results show that the mechanical properties of as-welded and hardening recovery provided by post weld heat treatment (HRPWHT) conditions are close. The HRPWHT provide a notorious improvement in mechanical properties in the fusion zone (FZ) as well as in the Inconel 718 side. However, it did not have any effect in the AL6XN side. Due to the aforementioned, the resistance of the weldment (IN718-AL6XN) is similar in both conditions. For the tension tests, the weldments to which heat treatment was not applied exhibit the failure in the weld bead, on the other side, the weldments with HRPWHT fractured along the fusion line at the AL6XN side. The failure in the weld bead was attributed to the presence of detrimental secondary phases (NbC and Laves), which were partially dissolved with the HRPWHT. This provides similar mechanical properties of the dissimilar welded joints. The most evident difference was observed in the elongation percentage, which was higher in the as-welded condition (14.05%) in comparison with the HRPWHT condition (10.8%).

Thermal efficiency in welding of AA6061-T6 alloy by modified indirect electric arc and digitalization of current signals

The results of thermal efficiency on welding using the modified indirect electric arc technique [Ambriz RR, Barrera G, García R. S&I. 2006;11:10–17] of the 6061-T6 aluminium alloy are presented. These values are in the range of 90–94%, depending on the preheat temperature and were obtained by means of a heat balance that considers the heat input, the amount of molten mass of the welding profiles, and welding parameters during the joining, giving particular emphasis to the data collected during the digitalization of the arc current. Also, some dimensionless parameters were employed in order to determine the approximation grade of the molten pool, the heat-affected zone, and their corresponding approximations to the experimental results.