Cracking susceptibility of aluminum alloys during laser welding

The influence of laser parameters in welding aluminum alloys was studied in order to reduce hot cracking. The extension of cracks at the welding surface was used as a cracking susceptibility (CS) index. It has been shown that the CS changes with changing welding velocity for binary Al-Cu alloys. In general, the CS index increased until a maximum velocity and then dropped to zero, generating a typical lambda-curve. This curve is due to two different mechanisms: 1) the refinement of porosities with increasing velocity and 2) the changes in the liquid fraction due to decreasing microsegregation with increasing velocities

Fermentação ruminal e eficiência microbiana em bezerros holandeses alimentados com dietas contendo diferentes níveis de concentrado Ruminal fermentation and microbial efficiency in Holstein calves fed diets with different concentrate levels

RESUMO - Este trabalho foi realizado para avaliar os efeitos de diferentes níveis de concentrado sobre os parâmetros da fermentação ruminal, as digestibilidades aparente, total, ruminal e intestinal de N, a eficiência microbiana e o balanço de N. Cinco bezerros holandeses, inteiros, fistulados no rúmen e abomaso, com idade média inicial de 5,8±0,7 meses e 107,4±11,0 kg PV médio inicial, foram distribuídos em quadrado latino 5x5 (tratamento x período). Os animais foram alojados em baias individuais e alimentados à vontade com dietas contendo 30,0; 45,0; 60;0; 75,0; e 90,0% de concentrado, com base na MS, em rações contendo como volumoso, o feno de capim coast-cross e no concentrado, o farelo de soja, fubá de milho. Os valores de pH foram influenciados pelos níveis de concentrado das rações, e , 11,3 horas após a alimentação, foram estimandos os valores mínimos de 6,10; 5,89; 5,67; 5,46; e 5,24, para as rações com níveis de 30,0; 45,0; 60,0; 75,0; e 90,0%de concentrado nas rações, respectivamente. A concentração de amônia ruminal reduziu linearmente, em função dos tempos pós-alimentação, apresentando comportamento quadrático, com valores mínimos de 6,84; 7,14; 7,63; 7,82; 8,09; e 8,00 mg/dL, para 86,31; 84,86; 83,41; 81,95; 77,59; e 68,86% de concentrado nas rações. O numero de protozoários ruminais reduziu linearmente com o aumento dos níveis de concentrado nas rações. A eficiência de síntese de compostos nitrogenados microbianos aumentou linearmente com os níveis de concentrado nas rações.<br>ABSTRACT - This work was conducted to evaluate the effects of different concentrate levels on the parameters of at ruminal fermentation, the apparent, total, ruminal and intestinal N digestibilities, the microbial efficiency and the N balance. Five rumen and abomasum fistulated bull Holstein calves, with an initial average age of 5.8±0.7 months and initial average of 107.4±11.0 kg LW were allotted to a 5x5 Latin square design (treatment x period). The animals were housed in individual stalls and full fed diets (DM basis) containing 30.0, 45.0, 60.0, 75,0 and 90.0% of concentrate.The diets were based on coast-cross grass hay as forage and soybean meal and corn ground grain in the concentrate. The pH values were affected by the concentrate levels of the diets, and , 11.3 hours post-feeding, the minimum values of 6.10, 5.89, 5.67, 5.46, and 5.24, respectively, were estimated for the diets with 30.0, 45.0, 60.0, 75.0 e 90.0% of concentrate in the diets, respectively. The ruminal ammonia concentration linearly decreased, in function of post-feeding time and showing quadratic behavior, with a minimum values of 6.84, 7.14, 7,40, 7.63, 7.82, 8.09, and 8.00 mg/dL, for 86.31, 84.86, 83.41, 80,50, 81.95, 77.59, and 68.86% of concentrate in the diets. The number of ruminal protozoa linearly reduced as the dietary concentrate levels increased. The efficiency of microbial nitrogenous compound synthesis linearly increased, as the concentrate levels in the diets increased