Weak-magnetic Nondestructive Testing for Crack Defect in Nickel-copper Alloy Bar

Aiming at the present situation that the existing nondestructive testing technology can not meet the requirement of crack detection of nickel-copper alloy bar,a weak-magnetic nondestructive testing method in the geomagnetic field is proposed.In this paper,the theory of weak magnetic detection of nickel-copper alloy bars and the distribution of magnetic anomalies at defects are firstly analyzed,and then the weak-magnetic testing was carried out on the Ni-Cu alloy bar with natural defects.The envelope analysis method was used to process the signals,and the feasibility of the weak magnetic detection of nickel-copper alloy bars was verified by metallographic microscope and scanning electron microscopy. The results show that the effective detection of cracks in Ni-Cu alloy bar is achieved by analyzing the distribution of magnetic anomalies on the surface of bar and combining with the results of threshold processing and envelope analysis of magnetic gradient signals, and the precision of crack detection can achieve micron-level.