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Steel materials, which are widely used in industry, undergo corrosion to varying degrees when exposed to environments such as the atmosphere, seawater, soil, and building materials. According to statistics, around one-third of the total steel production worldwide is lost each year due to corrosion. To ensure the proper use of steel products and extend their service life, corrosion protection techniques for steel have always received widespread attention. Hot-dip galvanizing is one of the effective methods for delaying environmental corrosion of steel materials. It involves immersing steel products whose surfaces have been cleaned and activated in molten zinc; through reactions and diffusion between iron and zinc, a zinc alloy coating with good adhesion is formed on the surface of the steel products. Compared with other metal protection methods, the hot-dip galvanizing process offers unparalleled advantages in terms of the protective properties that combine a physical barrier with electrochemical protection, the strength of adhesion between the coating and the substrate, the density of the coating, its durability, maintenance-free nature, and cost-effectiveness, as well as its adaptability to the shape and size of the products. Currently, hot-dip galvanized products mainly include steel plates, steel strips, steel wires, steel pipes, etc., among which hot-dip galvanized steel plates account for the largest proportion. For a long time, the hot-dip galvanizing process has been highly favored due to its low coating cost, excellent protective properties, and attractive appearance. It is widely used in industries such as automobiles, construction, home appliances, chemicals, machinery, petroleum, metallurgy, light industry, transportation, power generation, aviation, and marine engineering. Hot-dip galvanized bolts are available in regular types and those with threaded holes. Classified by head shape: there are hexagonal heads, round heads, square heads, countersunk heads, and so on. Among them, the hex head is the most commonly used. Hot-dip galvanized bolts are generally used with countersinks in areas where connections are required. It is a non-standard fastener; it has a U-shaped design, which is why it is called a U-bolt. Hot-dip galvanized bolts have threads at both ends that allow them to be connected to nuts. They are primarily used for securing tubular objects such as water pipes, or sheet-like components such as the leaf springs in cars. Since the way in which these bolts secure objects is similar to a person sitting on a horse, they are also known as horsehead bolts. For connection bolts used in steel structures, unless otherwise specified, hot-dip galvanized bolts are generally ordinary rough-grade Class C bolts. ①The shanks of grade A and B bolts are manufactured using lathes, resulting in a smooth surface; their dimensions are precise, and their material strength grade is 8.8. Their production and installation are complex, and they are relatively expensive, which is why they are rarely used. ② Grade C bolts are made from untreated round steel, with less precise dimensions; their material strength grade is either 4.6 or 4.8. Shear connections exhibit significant deformation, but they are easy to install and have low production costs; they are commonly used for tensile connections or as temporary fixations during installation. Magnetic particle testing of hot-dip galvanized bolts utilizes the interaction between the magnetic field leakage at defects in the bolts and magnetic particles. Due to the difference in magnetic permeability between potential defects in the bolts such as cracks, inclusions, and mixing, the magnetic field at the discontinuities in these materials becomes distorted after magnetization, resulting in magnetic flux leakage. This creates a magnetic field on the surface of the part, which in turn attracts magnetic particles and leads to their accumulation at the defect sites – forming magnetic traces. Under appropriate lighting conditions, hot-dip galvanized bolts reveal the location and shape of these defects; by observing and analyzing these accumulations of magnetic particles, it is possible to identify and eliminate defective items.