Study on bimetallic bronze swords in ancient China

Abstract

As early as in Shang Dynasty (1600 - 1100BC) of China, there appeared bimetallic weapons formed by forged anode iron and bronze. This was the earliest combinative metal weapon in China. The formulas of Liu - chi in the K' ao Kung Chi, Zhou Li, specify the copper and tin contents of bronze according to various kinds of bronze articles. The K' ao Kung Chi, Zhou Li, was recorded in the Eastern Zhou (770 -221 BC)period,which showed that ancient Chinese had fully understood the relationship between bronze alloy and its properties at least in Eastern Zhou period. They could change the copper or tin content to get good bronzes. The bimetallic bronze weapons produced in Eastern Zhou were the creative application of the relationship between alloy composition and its properties. The blade of bimetallic bronze sword was cast with different composition of alloy from the cutting edge. In this paper, the research on them was introduced with the help of modern examinations and simulation experiments. It can been scan that the blade and cutting edge were all jointed with mortise and tenon from the cross section of fragmetns. The compositions of blade and cutting edge were tested by XRF. The lower - tin bronze formed blade with good toughness and the higher - tin bronze formed cutting edge with high hardness and strength. Microstructures were obseved by microscope and found that the normal cast dendrite of bronze is seen on the cutting edge and blade. The structure of blade is much coarser than that of the cutting edge. From the microstructure, it could be concluded that the cutting edge was not treated by heat after cast for its dendrite was clear and fine. The blade should be annealed in high temperature after cast for its dendrite was not clear and became coarse. After annealing, the brittle delta phase in the blade reduced, while the plasticity and toughness of blade increased evidently, resulting in a good resistance to shock. After some simulation experiments, we successfully restored the making technology and reproduced some bimetallic swords. Firstly, making two clay moulds to cast a blade in 88% copper, 10% tin and 2% lead with tenon. And then,making two clay moulds for cutting edge with the bronze blade in the cavity. Liquid bronze in 78% copper,20% tin and 2% lead was poured into the cavity. After solidification and shrinkage,the cutting edge tightly surrounded the tenon of spine. Finally, moved the assembly of spine and cutting edge out of the clay mould when it is cooled. Polishing the sword surface and cutting edge. Putting it into the clay mould again for casting the guard, grip and pommel. Then a bimetallic sword was finished. By casting in steps, a bimetallic sword was produced with both rigidity and flexibility. Making bimetallic swords show that the influence of tin content on bronze mechanical properties had been fully understood by the Chinese ancients.

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