某型航空机载光电设备试制过程中，在冲击摸底试验后，设备中镁合金材料的主承重件连接盘出现裂纹。通过宏观分析、化学成分分析、金相检验及应力应变测试等方法，对连接盘产生裂纹的原因进行了分析。结果表明：由于连接盘采用手工铸造工艺，不可控因素较多，导致在个别连接盘加强筋内部产生大量缩松缺陷，影响了铸件的连续性，使得零件的承载能力及抗疲劳能力降低，试验时受到力的作用后在内部缺陷处萌生裂纹源，裂纹扩展，最终导致连接盘加强筋过载开裂。

During the trial production of a certain type of airborne optoelectronic equipment, cracks appeared on the connecting plate of main bearing part of magnesium alloy materials in the equipment after impact test. The causes of cracks in the connecting plate were analyzed by means of macro analysis, chemical composition analysis, metallographic examination and stress strain test. The results show that there were many uncontrollable factors in the manual casting process of connecting plate, which led to a large number of shrinkage defects in the internal stiffeners of connecting plate, affecting the continuity of casting, and reducing the bearing capacity and anti fatigue ability of the part. During the test, under the action of force, the crack source initiated in internal defects, and the crack propagation eventually led to the overload cracking of connecting plate stiffeners.