I have the following two-axis line chart created in ggplot2:

#data
datos_graficos <- data.frame(
  Arena = c(20,25,30,35,40,45,50),
  Media_Mg = c(0.3050000,0.3025000,0.2775000,0.3157143,0.2887500,0.2928571,0.3225000),
  SE_Mg = c(0.02160155,0.02160155,0.02160155,0.02309303,0.02160155,0.02309303,0.02160155),
  Rangos_Mg = c("a","a","a","a","a","a","a"),
  Media_Fe = c(27.00000,30.25000,68.87500,67.42857,85.12500,63.42857,71.25000),
  SE_Fe =c(11.60294,11.60294,11.60294,12.40406,11.60294,12.40406,11.60294),
  Rangos_Fe = c("b","bc","a","a","a","ab","a")
)

#plotting in ggplot2
escala_factor <- max(datos_graficos$Media_Fe)/max(datos_graficos$Media_Mg)#variable de la izquierdo/derecho

library(ggplot2)
library(ggrepel)
ggplot(datos_graficos, aes(x = Arena)) +
  #eje y izquierdo: hierro
  geom_line(
    aes(y = Media_Fe,
        group = 1, 
        color = "Hierro",
        linetype = "solid"
    ), 
    size = 0.8) + 
  geom_point(
    aes(y = Media_Fe, color = "Hierro"), 
    size = 2) + #puntos para hierro
  geom_text_repel(
    aes(y = Media_Fe, label = Rangos_Fe),
    color = "black", size = 3) + #letras para hierro
  geom_errorbar(
    aes(y = Media_Fe, 
        ymin = Media_Fe - SE_Fe, 
        ymax = Media_Fe + SE_Fe, 
        color = "Hierro"), 
    width = 0.2, size = 0.5) + #barras de error para Hierro
  #eje y derecho: magnesio
  geom_line(
    aes(y = Media_Mg * escala_factor, 
        group = 1, 
        color = "Magnesio",
        linetype = "dashed"
    ), size = 0.8) + #linea para magnesio
  geom_point(
    aes(y = Media_Mg * escala_factor, 
        color = "Magnesio"), 
    size = 2) + #puntos para magnesio
  geom_text_repel(
    aes(y = Media_Mg * escala_factor,
        label = Rangos_Mg), 
    color = "black", size = 3) + #letras para magnesio
  geom_errorbar(
    aes(y = Media_Mg * escala_factor,
        ymin = Media_Mg * escala_factor - SE_Mg * escala_factor, 
        ymax = Media_Mg * escala_factor + SE_Mg * escala_factor, 
        color = "Magnesio"), 
    width = 0.2, size = 0.5) + #barras de error para magnesio
  scale_y_continuous(
    name = "Hierro (mg/kg)", #eje y izquierdo
    sec.axis = sec_axis(#eje y derecho
      ~./escala_factor, name = "Magnesio (%)",
    ),
    limits = c(0, 100)) + #limites al eje y izquierdo
  labs(x = "Arena (%)") +
  #leyenda
  scale_color_manual(
    values = c("Hierro" = "black", "Magnesio" = "black"),
    guide = "none") +
  guides(
    linetype = guide_legend(
      title = "Elemento", 
      labels = c("Magnesio", "Hierro"),
      values = c("Magnesio" = "dashed", "Hierro" = "solid"),
    )) +
  theme(
    axis.title.y = element_text(size = 10),
    axis.title.y.right = element_text(size = 10,color="black"),
    axis.text = element_text(size = 8),
    legend.key.width = unit(1, 'cm'), 
    legend.text = element_text(size = 8), 
    axis.title.y.left=element_text(color="black"),
    axis.text.y.left=element_text(color="black"),
    axis.text.y.right=element_text(color="black")
  )

The code above generates this chart:

Problem: In the legend, how to change the name from “dashed” to “Magnesio” and from “solid” to “Hierro”? The line drawn as dashed is actually for Hierro, the line drawn as solid is really for Magnesio.

Thank you very much for the help.