C. P. Chou

Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys

This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor (BPM). The welding parameters include the modes of laser output (pulsed wave and continuous wave), welding speed, shield gas flow, welding bead structure, and focusing distance. The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type. The crack in the welding bead reduced with decreasing welding speed. The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material. Weld morphology during the experimental process revealed the proper flow of shield gas. The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.

Laser induced popcornlike conformational transition of nanodiamond as a nanoknife

Nanodiamond (ND) is surrounded by layers of graphite on its surface. This unique structure feature creates unusual fluorescence spectra, which can be used as an indicator to monitor its surface modification. Meanwhile, the impurity, nitroso (CNO) inside the ND can be photolyzed by two-photon absorption, releasing NO to facilitate the formation of a sp3 diamond structure in the core of ND and transforming it into a sp2 graphite structure. Such a conformational transition enlarges the size of ND from 8to90nm, resulting in a popcornlike structure. This transition reaction may be useful as nanoknives in biomedical application.

Development of a Growth-Hormone-Conjugated Nanodiamond Complex for Cancer Therapy

It is highly desirable to develop a therapeutic, observable nanoparticle complex for specific targeting in cancer therapy. Growth hormone (GH) and its antagonists have been explored as cancer cell‐targeting molecules for both imaging and therapeutic applications. In this study, a low toxicity, biocompatible, therapeutic, and observable GH–nanoparticle complex for specifically targeting growth hormone receptor (GHR) in cancer cells was synthesized by conjugating GH with green fluorescence protein and carboxylated nanodiamond. Moreover, we have shown that this complex can be triggered by laser irradiation to create a “nanoblast” and induce cell death in the A549 non‐small‐cell lung cancer cell line via the apoptotic pathway. This laser‐mediated, cancer‐targeting platform can be widely used in cancer therapy.

Hot Cracking in AZ31 and AZ61 Magnesium Alloy

This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS) was used for component analysis. Results showed that AI content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in AI content, causing higher liquid Mg-alloy rich AI content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone (PMZ). In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher (6 wt%) AI content and produced much liquefied Mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied Mg17Al12 were pulled apart and hot cracks formed at weld metal HAZ due to the augmented strain. Since AZ31 had half the AI content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length (TCL) in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of AI during the welding process, which resulted in lower overall AI content. Consequently, shorter hot cracks exhibited in three thermal cycles. It was found the AI content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.

The Influence of Aluminum Content of AZ61 and AZ80 Magnesium Alloys on Hot Cracking

This study aims to investigate how aluminum content in magnesium alloys AZ61 and AZ80 impacts the hot cracking susceptibility of magnesium alloys. Differences in aluminum content are known to influence the total crack length of hot cracking. Magnesium alloy AZ61s total crack length was the longest in one thermal cycle, while AZ80s total crack length increased as the number of thermal cycles increased. The most significant difference between AZ61 and AZ80 was the hot crack at the heat-affected zone (HAZ). As the number of heat inputs increased, the grain would coarsen in the HAZ and precipitation started, which resulted in the accumulation of hot cracks at weld metal HAZ (W. M. HAZ). During the solidification of AZ80, which has higher aluminum content, the segregation of aluminum at the grain boundary caused Mg17Al12 to liquefy, increasing the length of hot cracks. Augmented strain caused miniature cracks between Mg17Al12 and grains. Therefore, aluminum content and augmented strain were found causes of hot cracking susceptibility in magnesium alloys.

Characterization of Hot Cracking Due to Welding of High-Strength Aluminum Alloys

The “Spot-Varestraint Test” was applied to assess the sensitivity of three aluminum alloys–A2024-T351, A2219-T87, and A7050-T6–to hot cracking from welding. The results indicate that the number of cracks increases with increasing augmented strain. This phenomenon occurs in both the fusion and the heat-affected zones. The number of thermal cycles also has a significant influence on the heat-affected zone; the number of hot cracks increases, especially in the heat-affected zone of the metal weld, with increasing number of thermal cycles. The compositions of these three alloys show that A2024 and A7050 have similar tendencies to be subject to hot cracking, greater than A2219. With increasing number of thermal cycles, the hot cracks show the same tendency, A2024 > A7050 > 2219.