**1. Introduction**

In the hush service environment, such as the nuclear power plant's primary water reactor, the performance of single metal materials is difficult to meet the requirement. Composite materials can ensure that the components have two or more of the properties of lightweight, high strength, good toughness, corrosion resistance, human body compatibility, and low cost, which has become a direction of current material development [1,2]. Welding is an important process for joining materials, for example, welding is indispensable for the assembly of high-temperature shape memory alloys [3], and it can also perform metallurgical bonding of high-entropy alloy workpieces [4]. However, the huge differences of dissimilar materials, especially in the microstructure, physical and chemical properties, which leads to the production of intermetallic compounds and the large residual stresses during the fusion welding process. Thus, the performance of the bonding area will be reduced [5–7]. To obtain a good metallurgical bond between dissimilar materials, researchers consider using solid-state welding processes for welding dissimilar materials, such as diffusion welding, friction stir welding [8], ultrasonic welding [9], and impact welding (explosive welding [10], magnetic pulse welding [11], etc.). The impact welding temperature is relatively low, and the thermal cycle time is extremely short. In theory, it can be widely used for welding between any metals. Metal cladding is already a common process conducted with explosive welding.

In recent years, there has been an increasing demand for connections between similar or dissimilar metal thin foils, especially in the fields of battery electrodes, special medical materials, metal anti-corrosion coatings, and the coating of heat dissipation layers of semiconductor materials. For example, the electrodes of the heart-pace maker need to be optimized with a good weld between aluminium and titanium. However, the solid-state welding technologies have certain limitations in the connection of dissimilar metal foils. Ultrasonic welding, as shown in Figure 1, produces surface indentation, and friction welding leads to layered intermetallic compounds [12,13]. In 2009, Daehn and Lippold [14] from The Ohio State University in the United States proposed a non-contact welding method with laser as the energy source—Laser impact welding. This process could realize solid metallurgical bonding between dissimilar metal foils with a thickness of millimeters/micrometers, with precise positioning and flexible as well as adjustable welding area size.

**Figure 1.** (**a**) Surface indentation of ultrasonic welding (reproduced from [9], with permission of Elsevier 2020); (**b**) Intermetallic compound layer with friction stir welding (reproduced from [15], with permission of Elsevier 2015).

As a new type of solid-state welding process, laser impact welding is still in the laboratory process exploration stage. This review summarizes the progress of the laser impact welding process and the results achieved at this stage from the mechanism of impact welding, the process of impact welding, the structure, and performance of the impact welded joint. It also proposes the development direction of the laser impact welding process and provides its maturity reference.
