Spray deposition is a novel manufacturing process, which is currently being developed for producing near-net-shape preforms. Spray deposition involves the creation of a spray of droplets by a gas atomizer and the consolidation of these droplets on a substrate to create a preform. In order to maximize the metallurgical benefits of spray deposition, a thorough study of the solidification process is important. In this study, 7075 Al alloy is atomized by high velocity argon gas and atomized droplets are collected on the fixed copper substrate. The microstructure of over spray powder and the preform are studied. Spray atomization produces various sizes of droplets, ranging from 5 to 300 mu m. A variety of microstructures are observed for different size of powders. Microstructural changes occur due to the difference in the cooling rates of the atomized droplets. The cooling rate of the fine droplets is high compared with coarse droplets. Generally the cooling rate of the droplet changes from 10~2 to 10~6 K s~(-1). In the spray deposition the preform shows equiaxed grains, while the size of the grain changes from bottom to top of the preform. The grain size measurements at the bottom, centre and top of the preform gives 25, 40 and 20 mu m respectively. This happens because of the fact that different portions of the preform experiences different cooling rates. The bottom and top of the preform have high cooling rate compared with the centre portion.
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机译：喷雾沉积是一种新颖的制造工艺，目前正在开发该工艺以生产接近最终形状的瓶坯。喷雾沉积涉及通过气体雾化器产生液滴的喷雾以及将这些液滴固结在基底上以形成预成型坯。为了最大化喷雾沉积的冶金学益处，对固化过程进行透彻的研究很重要。在这项研究中，7075铝合金被高速氩气雾化，雾化的液滴被收集在固定的铜基板上。研究了喷涂粉末和预成型坯的微观结构。喷雾雾化产生各种大小的液滴，范围从5到300微米。对于不同尺寸的粉末，观察到各种微观结构。由于雾化液滴的冷却速率不同，会发生微结构变化。与粗液滴相比，细液滴的冷却速率高。通常，液滴的冷却速率从10〜2变为10〜6 K s〜（-1）。在喷涂过程中，预成型坯显示等轴晶粒，而晶粒的大小从预成型坯的底部到顶部变化。在预成型坯的底部，中心和顶部的粒度测量分别为25、40和20μm。发生这种情况的原因是，预成型件的不同部分经历了不同的冷却速度。与中央部分相比，预成型坯的底部和顶部具有较高的冷却速度。
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