O. Marcelo Suárez

Thermomechanical Effects on Aluminum Matrix Composites Reinforced with AlB2 Particles

Aluminum matrix composites (AMCs) reinforced with aluminum diboride (AlB 2) particles are obtained through a casting process. A mixture design experiment combined with split-split plot experiment helped to assess the significance of the effects of cold work on precipitation hardening prior to aging. Both cold work and aging allowed higher microhardness of the composite matrix, which is further increased by higher levels of boron and copper. Microstructure analysis showed a good distribution of reinforcements and revealed a grain subdivision pattern due to cold work. Tensile tests helped corroborate the microhardness measurements. Fracture surface analysis showed a predominantly mixed brittle—ductile mode.

Corrosion Fatigue of High-Strength Aircraft Structural Alloys

Results of corrosion fatigue characterization of AA7075-T6 and AF1410 steel under different simulated marine environments and loading conditions are presented. In comparison with baseline tests conducted in laboratory air, corrosion fatigue experiments performed at 1-Hz frequency in the presence of 1% NaCl environment indicated a substantial reduction in fatigue lifetime in the case of AA7075-T6, whereas AF1410 corrosion fatigue life was found to be statistically unaffected at 1-Hz frequency in the presence of 1% and 3.5%NaCl. However, a reduction of frequency to 0.5 Hz significantly reduced the lifetime of AF1410 steel. On the other hand, Cd-plated AF1410 tested to study fatigue characteristics in a hydrogen-rich metal surface environment yielded minimal change in the lifetime. Atomic force microscope analysis was performed to discern features in fracture surface morphology leading to changes in lifetime of AF1410 and AA7075-T6 alloys.

Synthesis and Characterization of Mechanically Alloyed Al/AlxMg1-xB2 Composites

The use of high energy ball milling (HEBM) was investigated as an alternative method to synthesize aluminum matrix composites reinforced with AlxMg|.xB2 particles. HEBM allowed achieving appropriate mixing and wettability between the composite components. After a 900°C treatment under vacuum, the resulting material had a mixed microstructure of dispersoids and submicron AIxMgi.xB2(hereon also referred as (AIMg)B2) particles embedded in the Al matrix containing also β (Al3Mg2) + Al eutectic. After processing the size distribution of AlxMg|.xB2 particles included large particles (<23μηι) and submicron ones. Vickers microhardness measured on the composite matrix revealed that the highest matrix hardness was obtained in samples containing 5 wt.% AlxMgi.xB2 where larger amounts of nanosized reinforcement particles were present. X-ray diffraction studies showed the formation of AlxMgi.xB2 in the mechanically alloyed composites. In summary, the results buttressed the feasibility of fabricating a stronger Al-based composite via HEBM.

Fatigue and hydrogen embrittlement evaluation of AF1410 steel

AF1410 steel subject to lateral one-sided electrolytic hydrogen-charging and tested under fatigue at a stress ratio of 0.4 and at 1 Hz loading frequency displayed up to four times higher crack growth rate than specimens evaluated without exposure to hydrogen. Additionally, the hydrogen-attacked side underwent a change in the fracture mode from ductile to brittle, which can be either of intergranular, transgranular or quasi-cleavage nature. Scanning electron microscope and atomic force microscope studies as well as fracture surface analysis were conducted to correlate the fracture modes with the hydrogen embrittlement effects on the steel. Since hydrogen did not permeate the entire thickness of the specimens, the experiments provided a more realistic approach to the study of large aircraft components in marine service conditions.

Characterization of sputtered Al-B-Si thin films produced with composite targets for device applications

Abstract Sputtered films were deposited over glass and silicon (Si) substrates by using homemade centrifuged aluminum (Al) targets containing boron (B) AlB2 and AlB12 particles as their constituents. Additional films were produced with an as-received aluminum target for comparison purposes. The composite targets were mounted in the magnetron sputtering system working at varying discharge powers, ranging from 200 to 450 W, to produce films with the smallest surface roughness. This roughness analysis showed that films deposited from the composite targets (fabricated by centrifugal casting) possessed lower surface roughness than the pure aluminum films if they were deposited over silicon substrates. Also, preliminary studies of film structure and mechanical properties revealed that the films produced with the composite targets had smaller grain size, dominant compression stresses, higher disorder in the crystalline structure, and higher hardness and elastic modulus, when compared with the films produced with the pure aluminum target.

Tribological Comparative Study of the Effect of Boride and Silicon Particles on Aluminum Matrix Composite

An AI-Si-Sn alloy and an Al-B-Sn composite intended for bearing applications were manufactured by centrifugal casting and their resulting tribological properties were compared. Microstructure gradients of silicon particles and boride dispersoids were observed on both materials, increasing from the internal to the external casting zones. Superficial hardness and pin-on-disk wear tests performed showed a higher hardness and lower wear coefficient in the external regions. The boride-reinforced composite exhibited lower wear and higher hardness than the aluminum-siliconbased alloy.

Raising awareness on materials recycling using undergraduate engineering research

Undergraduate research in engineering was used as a means of raising awareness on materials recycling and alternative recycled material products and processes. Over a three-year period, the authors hosted undergraduate researchers to work on rubber and polymer concrete, rubber-sandwich structures and recycled rubber materials for road embankments and retaining wall backfills. This paper discusses the outcomes of this endeavour, which not only included minority participation in undergraduate research to improve retention but also engaged students in materials recycling through exploratory research on technological advances. It also provided them with a forum to actively participate in the dissemination of results to local government authorities.